Electromagnetic tracking with augmented reality systems

ABSTRACT

Head-mounted augmented reality (AR) devices can track pose of a wearer&#39;s head to provide a three-dimensional virtual representation of objects in the wearer&#39;s environment. An electromagnetic (EM) tracking system can track head or body pose. A handheld user input device can include an EM emitter that generates an EM field, and the head-mounted AR device can include an EM sensor that senses the EM field. EM information from the sensor can be analyzed to determine location and/or orientation of the sensor and thereby the wearer&#39;s pose. The EM emitter and sensor may utilize time division multiplexing (TDM) or dynamic frequency tuning to operate at multiple frequencies. Voltage gain control may be implemented in the transmitter, rather than the sensor, allowing smaller and lighter weight sensor designs. The EM sensor can implement noise cancellation to reduce the level of EM interference generated by nearby audio speakers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/495,597, filed Apr. 24, 2017, entitled ELECTROMAGNETIC TRACKING WITHAUGMENTED REALITY SYSTEMS, which claims the benefit of priority to U.S.Patent Application No. 62/328,003, filed Apr. 26, 2016, entitled SYSTEMSAND METHODS FOR AUGMENTED REALITY, and to U.S. Patent Application No.62/479,111, filed Mar. 30, 2017, entitled ELECTROMAGNETIC TRACKING WITHAUGMENTED REALITY SYSTEMS; all of the foregoing are hereby incorporatedby reference herein in their entireties.

BACKGROUND Field

The present disclosure relates to systems and methods to localizeposition or orientation of one or more objects in the context ofaugmented reality systems.

Modern computing and display technologies have facilitated thedevelopment of systems for so called “virtual reality” or “augmentedreality” experiences, wherein digitally reproduced images or portionsthereof are presented to a user in a manner wherein they seem to be, ormay be perceived as, real. A virtual reality, or “VR”, scenariotypically involves presentation of digital or virtual image informationwithout transparency to other actual real-world visual input; anaugmented reality, or “AR”, scenario typically involves presentation ofdigital or virtual image information as an augmentation to visualizationof the actual world around the user.

SUMMARY

Head-mounted augmented reality (AR) devices can track the pose of thewearer's head (or other body part) to be able to provide athree-dimensional virtual representation of objects in the wearer'senvironment. Embodiments of an electromagnetic (EM) tracking system canbe used to track head pose or body gestures. For example, a handhelduser input device can include an EM emitter and the head-mounted ARdevice can include an EM sensor. In some implementations, the EM emittergenerates an EM field that can be sensed by the EM sensor. EMinformation from the sensor can be analyzed to determine location and/ororientation of the sensor and thereby the wearer's head pose. The EMemitter and sensor may utilize time division multiplexing (TDM) ordynamic frequency tuning that allows the tracking system to operate atmultiple frequencies. Voltage gain control can be implemented in thetransmitter, rather than the sensor, allowing smaller and light weightsensor designs. The EM sensor can implement noise cancellation to reducethe level of EM interference generated by nearby audio speakers

An embodiment of a head-mounted display system comprises a displaypositionable in front of eyes of a wearer; an electromagnetic (EM) fieldemitter configured to generate a magnetic field having a frequency; anEM sensor configured to sense the magnetic field at the frequency; and aprocessor programmed to: receive signals from the EM sensor indicativeof a sensed magnetic field; and analyze the received signals todetermine a position or an orientation of the EM sensor.

An embodiment of an electromagnetic (EM) tracking system comprises an EMfield emitter comprising a first transmitter coil configured to generatea first magnetic field having a first frequency, a second transmittercoil configured to generate a second magnetic field having a secondfrequency, and a third transmitter coil configured to generate a thirdmagnetic field having a third frequency, the EM field emitter comprisinga first time division multiplexed (TDM) circuit configured to switchpower among the first transmitter coil, the second transmitter coil, andthe third transmitter coil. A head-mounted augmented reality displaydevice can comprise embodiments of the EM tracking system.

An embodiment of an electromagnetic (EM) tracking system comprises an EMfield emitter comprising an automatic gain control (AGC) circuit and atransmitter coil; and an EM sensor without an AGC circuit, the EM sensorcomprising a sensor coil. A head-mounted augmented reality displaydevice can comprise embodiments of the EM tracking system.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Neitherthis summary nor the following detailed description purports to defineor limit the scope of the inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an illustration of an augmented reality scenario withcertain virtual reality objects, and certain physical objects viewed bya person.

FIGS. 2A-2D schematically illustrate examples of a wearable system.

FIG. 3 schematically illustrates coordination between cloud computingassets and local processing assets.

FIG. 4 schematically illustrates an example system diagram of anelectromagnetic (EM) tracking system.

FIG. 5 is a flowchart describing example functioning of an embodiment ofan electromagnetic tracking system.

FIG. 6 schematically illustrates an example of an electromagnetictracking system incorporated with an AR system.

FIG. 7 is a flowchart describing functioning of an example of anelectromagnetic tracking system in the context of an AR device.

FIG. 8 schematically illustrates examples of components of an embodimentof an AR system.

FIGS. 9A-9F schematically illustrate examples of a quick release module.

FIG. 10 schematically illustrates a head-mounted display system.

FIGS. 11A and 11B schematically illustrate examples of electromagneticsensing coils coupled to a head-mounted display.

FIGS. 12A-12E schematically illustrate example configurations of aferrite core that can be coupled to an electromagnetic sensor.

FIG. 13A is a block diagram that schematically illustrates an example ofan EM transmitter circuit (EM emitter) that is frequency divisionmultiplexed (FDM).

FIG. 13B is a block diagram that schematically illustrates an example ofan EM receiver circuit (EM sensor) that is frequency divisionmultiplexed.

FIG. 13C is a block diagram that schematically illustrates an example ofan EM transmitter circuit that is time division multiplexed (TDM).

FIG. 13D is a block diagram that schematically illustrates an example ofa dynamically tunable circuit for an EM transmitter.

FIG. 13E is a graph showing examples of resonances that can be achievedby dynamically tuning the circuit shown in FIG. 13D.

FIG. 13F illustrates an example of a timing diagram for a time divisionmultiplexed EM transmitter and receiver.

FIG. 13G illustrates an example of scan timing for a time divisionmultiplexed EM transmitter and receiver.

FIG. 13H is a block diagram that schematically illustrates an example ofa TDM receiver in EM tracking system.

FIG. 13I is a block diagram that schematically illustrates an example ofan EM receiver without automatic gain control (AGC).

FIG. 13J is a block diagram that schematically illustrates an example ofan EM transmitter that employs AGC.

FIGS. 14 and 15 are flowcharts that illustrate examples of pose trackingwith an electromagnetic tracking system in a head-mounted AR system.

FIGS. 16A and 16B schematically illustrates examples of components ofother embodiments of an AR system.

FIG. 17A schematically illustrates an example of a resonant circuit in atransmitter in an electromagnetic tracking system.

FIG. 17B is a graph that shows an example of a resonance at 22 kHz inthe resonant circuit of FIG. 17A.

FIG. 17C is a graph that shows an example of current flowing through aresonant circuit.

FIGS. 17D and 17E schematically illustrate examples of a dynamicallytunable configuration for a resonant circuit in an EM field transmitterof an electromagnetic tracking system.

FIG. 17F is a graph that shows examples of dynamically tuned resonancesby changing the value of the capacitance of capacitor C4 in the examplecircuit shown in FIG. 17E.

FIG. 17G is a graph that shows examples of the maximum current achievedat various resonant frequencies.

FIG. 18A is a block diagram that schematically shows an example of anelectromagnetic field sensor adjacent an audio speaker.

FIG. 18B is a block diagram that schematically shows an example of anelectromagnetic field sensor with a noise canceling system that receivesinput from both the sensor and the external audio speaker.

FIG. 18C is a graph that shows an example of how a signal can beinverted and added to cancel the magnetic interference caused by anaudio speaker.

FIG. 18D is a flowchart that shows an example method for cancelinginterference received by an EM sensor in an EM tracking system.

FIG. 19 schematically shows use of a pattern of lights to assist incalibration of the vision system.

FIGS. 20A-20C are block diagrams of example circuits usable withsubsystems or components of a wearable display device.

FIG. 21 is a graph that shows an example of fusing output from an IMU,an electromagnetic tracking sensor, and an optical sensor.

FIGS. 22A-22C schematically illustrate additional examples ofelectromagnetic sensing coils coupled to a head-mounted display.

FIGS. 23A-23C schematically illustrate an example of recalibrating ahead-mounted display using electromagnetic signals and an acousticsignal.

FIGS. 24A-24D schematically illustrate additional examples ofrecalibrating a head-mounted display using a camera or a depth sensor.

FIGS. 25A and 25B schematically illustrate techniques for resolvingposition ambiguity that may be associated with an electromagnetictracking system.

Throughout the drawings, reference numbers may be re-used to indicatecorrespondence between referenced elements. The drawings are provided toillustrate example embodiments described herein and are not intended tolimit the scope of the disclosure.

DETAILED DESCRIPTION

Overview of AR, VR and Localization Systems

In FIG. 1 an augmented reality scene (4) is depicted wherein a user ofan AR technology sees a real-world park-like setting (6) featuringpeople, trees, buildings in the background, and a concrete platform(1120). In addition to these items, the user of the AR technology alsoperceives that he “sees” a robot statue (1110) standing upon thereal-world platform (1120), and a cartoon-like avatar character (2)flying by which seems to be a personification of a bumble bee, eventhough these elements (2, 1110) do not exist in the real world. As itturns out, the human visual perception system is very complex, andproducing a VR or AR technology that facilitates a comfortable,natural-feeling, rich presentation of virtual image elements amongstother virtual or real-world imagery elements is challenging.

For instance, head-worn AR displays (or helmet-mounted displays, orsmart glasses) typically are at least loosely coupled to a user's head,and thus move when the user's head moves. If the user's head motions aredetected by the display system, the data being displayed can be updatedto take the change in head pose into account.

As an example, if a user wearing a head-worn display views a virtualrepresentation of a three-dimensional (3D) object on the display andwalks around the area where the 3D object appears, that 3D object can bere-rendered for each viewpoint, giving the user the perception that heor she is walking around an object that occupies real space. If thehead-worn display is used to present multiple objects within a virtualspace (for instance, a rich virtual world), measurements of head pose(e.g., the location and orientation of the user's head) can be used tore-render the scene to match the user's dynamically changing headlocation and orientation and provide an increased sense of immersion inthe virtual space.

In AR systems, detection or calculation of head pose can facilitate thedisplay system to render virtual objects such that they appear to occupya space in the real world in a manner that makes sense to the user. Inaddition, detection of the position and/or orientation of a real object,such as handheld device (which also may be referred to as a “totem”),haptic device, or other real physical object, in relation to the user'shead or AR system may also facilitate the display system in presentingdisplay information to the user to enable the user to interact withcertain aspects of the AR system efficiently. As the user's head movesaround in the real world, the virtual objects may be re-rendered as afunction of head pose, such that the virtual objects appear to remainstable relative to the real world. At least for AR applications,placement of virtual objects in spatial relation to physical objects(e.g., presented to appear spatially proximate a physical object in two-or three-dimensions) may be a non-trivial problem. For example, headmovement may significantly complicate placement of virtual objects in aview of an ambient environment. Such is true whether the view iscaptured as an image of the ambient environment and then projected ordisplayed to the end user, or whether the end user perceives the view ofthe ambient environment directly. For instance, head movement willlikely cause a field of view of the end user to change, which willlikely require an update to where various virtual objects are displayedin the field of the view of the end user. Additionally, head movementsmay occur within a large variety of ranges and speeds. Head movementspeed may vary not only between different head movements, but within oracross the range of a single head movement. For instance, head movementspeed may initially increase (e.g., linearly or not) from a startingpoint, and may decrease as an ending point is reached, obtaining amaximum speed somewhere between the starting and ending points of thehead movement. Rapid head movements may even exceed the ability of theparticular display or projection technology to render images that appearuniform and/or as smooth motion to the end user.

Head tracking accuracy and latency (e.g., the elapsed time between whenthe user moves his or her head and the time when the image gets updatedand displayed to the user) have been challenges for VR and AR systems.Especially for display systems that fill a substantial portion of theuser's visual field with virtual elements, it is advantageous if theaccuracy of head-tracking is high and that the overall system latency isvery low from the first detection of head motion to the updating of thelight that is delivered by the display to the user's visual system. Ifthe latency is high, the system can create a mismatch between the user'svestibular and visual sensory systems, and generate a user perceptionscenario that can lead to motion sickness or simulator sickness. If thesystem latency is high, the apparent location of virtual objects willappear unstable during rapid head motions.

In addition to head-worn display systems, other display systems canbenefit from accurate and low latency head pose detection. These includehead-tracked display systems in which the display is not worn on theuser's body, but is, e.g., mounted on a wall or other surface. Thehead-tracked display acts like a window onto a scene, and as a usermoves his head relative to the “window” the scene is re-rendered tomatch the user's changing viewpoint. Other systems include a head-wornprojection system, in which a head-worn display projects light onto thereal world.

Additionally, in order to provide a realistic augmented realityexperience, AR systems may be designed to be interactive with the user.For example, multiple users may play a ball game with a virtual balland/or other virtual objects. One user may “catch” the virtual ball, andthrow the ball back to another user. In another embodiment, a first usermay be provided with a totem (e.g., a real bat communicatively coupledto the AR system) to hit the virtual ball. In other embodiments, avirtual user interface may be presented to the AR user to allow the userto select one of many options. The user may use totems, haptic devices,wearable components, or simply touch the virtual screen to interact withthe system.

Detecting head pose and orientation of the user, and detecting aphysical location of real objects in space enable the AR system todisplay virtual content in an effective and enjoyable manner. However,although these capabilities are key to an AR system, but are difficultto achieve. In other words, the AR system can recognize a physicallocation of a real object (e.g., user's head, totem, haptic device,wearable component, user's hand, etc.) and correlate the physicalcoordinates of the real object to virtual coordinates corresponding toone or more virtual objects being displayed to the user. This generallyrequires highly accurate sensors and sensor recognition systems thattrack a position and orientation of one or more objects at rapid rates.Current approaches do not perform localization at satisfactory speed orprecision standards.

Thus, there is a need for a better localization system in the context ofAR and VR devices.

Example AR and VR Systems and Components

Referring to FIGS. 2A-2D, some general componentry options areillustrated. In the portions of the detailed description which followthe discussion of FIGS. 2A-2D, various systems, subsystems, andcomponents are presented for addressing the objectives of providing ahigh-quality, comfortably-perceived display system for human VR and/orAR.

As shown in FIG. 2A, an AR system user (60) is depicted wearing headmounted component (58) featuring a frame (64) structure coupled to adisplay system (62) positioned in front of the eyes of the user. Aspeaker (66) is coupled to the frame (64) in the depicted configurationand positioned adjacent the ear canal of the user (in one embodiment,another speaker, not shown, is positioned adjacent the other ear canalof the user to provide for stereo/shapeable sound control). The display(62) is operatively coupled (68), such as by a wired lead or wirelessconnectivity, to a local processing and data module (70) which may bemounted in a variety of configurations, such as fixedly attached to theframe (64), fixedly attached to a helmet or hat (80) as shown in theembodiment of FIG. 2B, embedded in headphones, removably attached to thetorso (82) of the user (60) in a backpack-style configuration as shownin the embodiment of FIG. 2C, or removably attached to the hip (84) ofthe user (60) in a belt-coupling style configuration as shown in theembodiment of FIG. 2D.

The local processing and data module (70) may comprise a power-efficientprocessor or controller, as well as digital memory, such as flashmemory, both of which may be utilized to assist in the processing,caching, and storage of data a) captured from sensors which may beoperatively coupled to the frame (64), such as image capture devices(such as cameras), microphones, inertial measurement units,accelerometers, compasses, GPS units, radio devices, and/or gyros;and/or b) acquired and/or processed using the remote processing module(72) and/or remote data repository (74), possibly for passage to thedisplay (62) after such processing or retrieval. The local processingand data module (70) may be operatively coupled (76, 78), such as via awired or wireless communication links, to the remote processing module(72) and remote data repository (74) such that these remote modules (72,74) are operatively coupled to each other and available as resources tothe local processing and data module (70).

In one embodiment, the remote processing module (72) may comprise one ormore relatively powerful processors or controllers configured to analyzeand process data and/or image information. In one embodiment, the remotedata repository (74) may comprise a relatively large-scale digital datastorage facility, which may be available through the internet or othernetworking configuration in a “cloud” resource configuration. In oneembodiment, all data is stored and all computation is performed in thelocal processing and data module, allowing fully autonomous use from anyremote modules.

Referring now to FIG. 3, a schematic illustrates coordination betweenthe cloud computing assets (46) and local processing assets, which may,for example reside in head mounted componentry (58) coupled to theuser's head (120) and a local processing and data module (70), coupledto the user's belt (308; therefore the component 70 may also be termed a“belt pack” 70), as shown in FIG. 3. In one embodiment, the cloud (46)assets, such as one or more server systems (110) are operatively coupled(115), such as via wired or wireless networking (wireless beingpreferred for mobility, wired being preferred for certain high-bandwidthor high-data-volume transfers that may be desired), directly to (40, 42)one or both of the local computing assets, such as processor and memoryconfigurations, coupled to the user's head (120) and belt (308) asdescribed above. These computing assets local to the user may beoperatively coupled to each other as well, via wired and/or wirelessconnectivity configurations (44), such as the wired coupling (68)discussed below in reference to FIG. 8. In one embodiment, to maintain alow-inertia and small-size subsystem mounted to the user's head (120),primary transfer between the user and the cloud (46) may be via the linkbetween the subsystem mounted at the belt (308) and the cloud, with thehead mounted (120) subsystem primarily data-tethered to the belt-based(308) subsystem using wireless connectivity, such as ultra-wideband(“UWB”) connectivity, as is currently employed, for example, in personalcomputing peripheral connectivity applications.

With efficient local and remote processing coordination, and anappropriate display device for a user, such as the user interface oruser display system (62) shown in FIG. 2A, or variations thereof,aspects of one world pertinent to a user's current actual or virtuallocation may be transferred or “passed” to the user and updated in anefficient fashion. In other words, a map of the world may be continuallyupdated at a storage location which may partially reside on the user'sAR system and partially reside in the cloud resources. The map (alsoreferred to as a “passable world model”) may be a large databasecomprising raster imagery, 3-D and 2-D points, parametric informationand other information about the real world. As more and more AR userscontinually capture information about their real environment (e.g.,through cameras, sensors, IMUs, etc.), the map becomes more and moreaccurate and complete.

With a configuration as described above, wherein there is one worldmodel that can reside on cloud computing resources and be distributedfrom there, such world can be “passable” to one or more users in arelatively low bandwidth form preferable to trying to pass aroundreal-time video data or the like. The augmented experience of the personstanding near the statue (e.g., as shown in FIG. 1) may be informed bythe cloud-based world model, a subset of which may be passed down tothem and their local display device to complete the view. A personsitting at a remote display device, which may be as simple as a personalcomputer sitting on a desk, can efficiently download that same sectionof information from the cloud and have it rendered on their display.Indeed, one person actually present in the park near the statue may takea remotely-located friend for a walk in that park, with the friendjoining through virtual and augmented reality. The system will need toknow where the street is, wherein the trees are, where the statue is—butwith that information on the cloud, the joining friend can download fromthe cloud aspects of the scenario, and then start walking along as anaugmented reality local relative to the person who is actually in thepark.

Three-dimensional (3-D) points may be captured from the environment, andthe pose (e.g., vector and/or origin position information relative tothe world) of the cameras that capture those images or points may bedetermined, so that these points or images may be “tagged”, orassociated, with this pose information. Then points captured by a secondcamera may be utilized to determine the pose of the second camera. Inother words, one can orient and/or localize a second camera based uponcomparisons with tagged images from a first camera. Then this knowledgemay be utilized to extract textures, make maps, and create a virtualcopy of the real world (because then there are two cameras around thatare registered).

So at the base level, in one embodiment a person-worn system can beutilized to capture both 3-D points and the 2-D images that produced thepoints, and these points and images may be sent out to a cloud storageand processing resource. They may also be cached locally with embeddedpose information (e.g., cache the tagged images); so the cloud may haveon the ready (e.g., in available cache) tagged 2-D images (e.g., taggedwith a 3-D pose), along with 3-D points. If a user is observingsomething dynamic, he may also send additional information up to thecloud pertinent to the motion (for example, if looking at anotherperson's face, the user can take a texture map of the face and push thatup at an optimized frequency even though the surrounding world isotherwise basically static). More information on object recognizers andthe passable world model may be found in U.S. Patent Pub. No.2014/0306866, entitled “System and method for augmented and virtualreality”, which is incorporated by reference in its entirety herein,along with the following additional disclosures, which related toaugmented and virtual reality systems such as those developed by MagicLeap, Inc. of Plantation, Fla.: U.S. Patent Pub. No. 2015/0178939; U.S.Patent Pub. No. 2015/0205126; U.S. Patent Pub. No. 2014/0267420; U.S.Patent Pub. No. 2015/0302652; U.S. Patent Pub. No. 2013/0117377; andU.S. Patent Pub. No. 2013/0128230, each of which is hereby incorporatedby reference herein in its entirety.

GPS and other localization information may be utilized as inputs to suchprocessing. Highly accurate localization of the user's head, totems,hand gestures, haptic devices etc. may be advantageous in order todisplay appropriate virtual content to the user.

The head-mounted device (58) may include displays positionable in frontof the eyes of the wearer of the device. The displays may comprise lightfield displays. The displays may be configured to present images to thewearer at a plurality of depth planes. The displays may comprise planarwaveguides with diffraction elements. Examples of displays, head-mounteddevices, and other AR components usable with any of the embodimentsdisclosed herein are described in U.S. Patent Publication No.2015/0016777. U.S. Patent Publication No. 2015/0016777 is herebyincorporated by reference herein in its entirety.

Examples of Electromagnetic Localization

One approach to achieve high precision localization may involve the useof an electromagnetic (EM) field coupled with electromagnetic sensorsthat are strategically placed on the user's AR head set, belt pack,and/or other ancillary devices (e.g., totems, haptic devices, gaminginstruments, etc.). Electromagnetic tracking systems typically compriseat least an electromagnetic field emitter and at least oneelectromagnetic field sensor. The electromagnetic field emittergenerates an electromagnetic field having a known spatial (and/ortemporal) distribution in the environment of wearer of the AR headset.The electromagnetic filed sensors measure the generated electromagneticfields at the locations of the sensors. Based on these measurements andknowledge of the distribution of the generated electromagnetic field, apose (e.g., a position and/or orientation) of a field sensor relative tothe emitter can be determined. Accordingly, the pose of an object towhich the sensor is attached can be determined.

Referring now to FIG. 4, an example system diagram of an electromagnetictracking system (e.g., such as those developed by organizations such asthe Biosense division of Johnson & Johnson Corporation, Polhemus, Inc.of Colchester, Vt., manufactured by Sixense Entertainment, Inc. of LosGatos, Calif., and other tracking companies) is illustrated. In one ormore embodiments, the electromagnetic tracking system comprises anelectromagnetic field emitter 402 which is configured to emit a knownmagnetic field. As shown in FIG. 4, the electromagnetic field emittermay be coupled to a power supply (e.g., electric current, batteries,etc.) to provide power to the emitter 402.

In one or more embodiments, the electromagnetic field emitter 402comprises several coils (e.g., at least three coils positionedperpendicular to each other to produce field in the X, Y and Zdirections) that generate magnetic fields. This magnetic field is usedto establish a coordinate space (e.g., an X−Y−Z Cartesian coordinatespace). This allows the system to map a position of the sensors (e.g.,an (X,Y,Z) position) in relation to the known magnetic field, and helpsdetermine a position and/or orientation of the sensors. In one or moreembodiments, the electromagnetic sensors 404 a, 404 b, etc. may beattached to one or more real objects. The electromagnetic sensors 404may comprise smaller coils in which current may be induced through theemitted electromagnetic field. Generally the “sensor” components (404)may comprise small coils or loops, such as a set of threedifferently-oriented (e.g., such as orthogonally oriented relative toeach other) coils coupled together within a small structure such as acube or other container, that are positioned/oriented to captureincoming magnetic flux from the magnetic field emitted by the emitter(402), and by comparing currents induced through these coils, andknowing the relative positioning and orientation of the coils relativeto each other, relative position and orientation of a sensor relative tothe emitter may be calculated.

One or more parameters pertaining to a behavior of the coils andinertial measurement unit (“IMU”) components operatively coupled to theelectromagnetic tracking sensors may be measured to detect a positionand/or orientation of the sensor (and the object to which it is attachedto) relative to a coordinate system to which the electromagnetic fieldemitter is coupled. In one or more embodiments, multiple sensors may beused in relation to the electromagnetic emitter to detect a position andorientation of each of the sensors within the coordinate space. Theelectromagnetic tracking system may provide positions in threedirections (e.g., X, Y and Z directions), and further in two or threeorientation angles. In one or more embodiments, measurements of the IMUmay be compared to the measurements of the coil to determine a positionand orientation of the sensors. In one or more embodiments, bothelectromagnetic (EM) data and IMU data, along with various other sourcesof data, such as cameras, depth sensors, and other sensors, may becombined to determine the position and orientation. This information maybe transmitted (e.g., wireless communication, Bluetooth, etc.) to thecontroller 406. In one or more embodiments, pose (or position andorientation) may be reported at a relatively high refresh rate inconventional systems. Conventionally an electromagnetic field emitter iscoupled to a relatively stable and large object, such as a table,operating table, wall, or ceiling, and one or more sensors are coupledto smaller objects, such as medical devices, handheld gaming components,or the like. Alternatively, as described below in reference to FIG. 6,various features of the electromagnetic tracking system may be employedto produce a configuration wherein changes or deltas in position and/ororientation between two objects that move in space relative to a morestable global coordinate system may be tracked; in other words, aconfiguration is shown in FIG. 6 wherein a variation of anelectromagnetic tracking system may be utilized to track position andorientation delta between a head-mounted component and a hand-heldcomponent, while head pose relative to the global coordinate system (sayof the room environment local to the user) is determined otherwise, suchas by simultaneous localization and mapping (“SLAM”) techniques usingoutward-capturing cameras which may be coupled to the head mountedcomponent of the system.

The controller 406 may control the electromagnetic field generator 402,and may also capture data from the various electromagnetic sensors 404.It should be appreciated that the various components of the system maybe coupled to each other through any electro-mechanical orwireless/Bluetooth means. The controller 406 may also comprise dataregarding the known magnetic field, and the coordinate space in relationto the magnetic field. This information is then used to detect theposition and orientation of the sensors in relation to the coordinatespace corresponding to the known electromagnetic field.

One advantage of electromagnetic tracking systems is that they producehighly accurate tracking results with minimal latency and highresolution. Additionally, the electromagnetic tracking system does notnecessarily rely on optical trackers, and sensors/objects not in theuser's line-of-vision may be easily tracked.

It should be appreciated that the strength of the electromagnetic fieldv drops as a cubic function of distance r from a coil transmitter (e.g.,electromagnetic field emitter 402). Thus, an algorithm may be used basedon a distance away from the electromagnetic field emitter. Thecontroller 406 may be configured with such algorithms to determine aposition and orientation of the sensor/object at varying distances awayfrom the electromagnetic field emitter. Given the rapid decline of thestrength of the electromagnetic field as the sensor moves farther awayfrom the electromagnetic emitter, best results, in terms of accuracy,efficiency and low latency, may be achieved at closer distances. Intypical electromagnetic tracking systems, the electromagnetic fieldemitter is powered by electric current (e.g., plug-in power supply) andhas sensors located within 20 ft radius away from the electromagneticfield emitter. A shorter radius between the sensors and field emittermay be more desirable in many applications, including AR applications.

Referring now to FIG. 5, an example flowchart describing a functioningof a typical electromagnetic tracking system is briefly described. At502, a known electromagnetic field is emitted. In one or moreembodiments, the magnetic field emitter may generate magnetic fieldseach coil may generate an electric field in one direction (e.g., X, Y orZ). The magnetic fields may be generated with an arbitrary waveform. Inone or more embodiments, the magnetic field component along each of theaxes may oscillate at a slightly different frequency from other magneticfield components along other directions. At 504, a coordinate spacecorresponding to the electromagnetic field may be determined. Forexample, the control 406 of FIG. 4 may automatically determine acoordinate space around the emitter based on the electromagnetic field.At 506, a behavior of the coils at the sensors (which may be attached toa known object) may be detected. For example, a current induced at thecoils may be calculated. In other embodiments, a rotation of coils, orany other quantifiable behavior may be tracked and measured. At 508,this behavior may be used to detect a position or orientation of thesensor(s) and/or known object. For example, the controller 406 mayconsult a mapping table that correlates a behavior of the coils at thesensors to various positions or orientations. Based on thesecalculations, the position in the coordinate space along with theorientation of the sensors may be determined.

In the context of AR systems, one or more components of theelectromagnetic tracking system may need to be modified to facilitateaccurate tracking of mobile components. As described above, tracking theuser's head pose and orientation may be desirable in many ARapplications. Accurate determination of the user's head pose andorientation allows the AR system to display the right virtual content tothe user. For example, the virtual scene may comprise a monster hidingbehind a real building. Depending on the pose and orientation of theuser's head in relation to the building, the view of the virtual monstermay need to be modified such that a realistic AR experience is provided.Or, a position and/or orientation of a totem, haptic device or someother means of interacting with a virtual content may be important inenabling the AR user to interact with the AR system. For example, inmany gaming applications, the AR system can detect a position andorientation of a real object in relation to virtual content. Or, whendisplaying a virtual interface, a position of a totem, user's hand,haptic device or any other real object configured for interaction withthe AR system can be known in relation to the displayed virtualinterface in order for the system to understand a command, etc.Conventional localization methods including optical tracking and othermethods are typically plagued with high latency and low resolutionproblems, which makes rendering virtual content challenging in manyaugmented reality applications.

In one or more embodiments, the electromagnetic tracking system,discussed in relation to FIGS. 4 and 5 may be adapted to the AR systemto detect position and orientation of one or more objects in relation toan emitted electromagnetic field. Typical electromagnetic systems tendto have a large and bulky electromagnetic emitters (e.g., 402 in FIG.4), which is problematic for head-mounted AR devices. However, smallerelectromagnetic emitters (e.g., in the millimeter range) may be used toemit a known electromagnetic field in the context of the AR system.

Referring now to FIG. 6, an electromagnetic tracking system may beincorporated with an AR system as shown, with an electromagnetic fieldemitter 602 incorporated as part of a hand-held controller 606. Thecontroller 606 can be movable independently relative to the AR headset(or the belt pack 70). For example, the user can hold the controller 606in his or her hand, or the controller could be mounted to the user'shand or arm (e.g., as a ring or bracelet or as part of a glove worn bythe user). In one or more embodiments, the hand-held controller may be atotem to be used in a gaming scenario (e.g., a multi-degree-of-freedomcontroller) or to provide a rich user experience in an AR environment orto allow user interaction with an AR system. In other embodiments, thehand-held controller may be a haptic device. In yet other embodiments,the electromagnetic field emitter may simply be incorporated as part ofthe belt pack 70. The hand-held controller 606 may comprise a battery610 or other power supply that powers that electromagnetic field emitter602. It should be appreciated that the electromagnetic field emitter 602may also comprise or be coupled to an IMU 650 component configured toassist in determining positioning and/or orientation of theelectromagnetic field emitter 602 relative to other components. This maybe especially advantageous in cases where both the field emitter 602 andthe sensors (604) are mobile. Placing the electromagnetic field emitter602 in the hand-held controller rather than the belt pack, as shown inthe embodiment of FIG. 6, helps ensure that the electromagnetic fieldemitter is not competing for resources at the belt pack, but rather usesits own battery source at the hand-held controller 606. In yet otherembodiments, the electromagnetic field emitter 602 can be disposed onthe AR headset and the sensors 604 can be disposed on the controller 606or belt pack 70.

In one or more embodiments, the electromagnetic sensors 604 may beplaced on one or more locations on the user's headset, along with othersensing devices such as one or more IMUs or additional magnetic fluxcapturing coils 608. For example, as shown in FIG. 6, sensors (604, 608)may be placed on one or both sides of the head set (58). Since thesesensors are engineered to be rather small (and hence may be lesssensitive, in some cases), having multiple sensors may improveefficiency and precision. In one or more embodiments, one or moresensors may also be placed on the belt pack 70 or any other part of theuser's body. The sensors (604, 608) may communicate wirelessly orthrough Bluetooth to a computing apparatus that determines a pose andorientation of the sensors (and the AR headset to which it is attached).In one or more embodiments, the computing apparatus may reside at thebelt pack 70. In other embodiments, the computing apparatus may resideat the headset itself, or even the hand-held controller 606. Thecomputing apparatus may in turn comprise a mapping database (e.g.,passable world model, coordinate space, etc.) to detect pose, todetermine the coordinates of real objects and virtual objects, and mayeven connect to cloud resources and the passable world model, in one ormore embodiments.

As described above, conventional electromagnetic emitters may be toobulky for AR devices. Therefore the electromagnetic field emitter may beengineered to be compact, using smaller coils compared to traditionalsystems. However, given that the strength of the electromagnetic fielddecreases as a cubic function of the distance away from the fieldemitter, a shorter radius between the electromagnetic sensors 604 andthe electromagnetic field emitter 602 (e.g., about 3 to 3.5 ft) mayreduce power consumption when compared to conventional systems such asthe one detailed in FIG. 4.

This aspect may either be utilized to prolong the life of the battery610 that may power the controller 606 and the electromagnetic fieldemitter 602, in one or more embodiments. Or, in other embodiments, thisaspect may be utilized to reduce the size of the coils generating themagnetic field at the electromagnetic field emitter 602. However, inorder to get the same strength of magnetic field, the power may be needto be increased. This allows for a compact electromagnetic field emitterunit 602 that may fit compactly at the hand-held controller 606.

Several other changes may be made when using the electromagnetictracking system for AR devices. Although this pose reporting rate israther good, AR systems may require an even more efficient posereporting rate. To this end, IMU-based pose tracking may (additionallyor alternatively) be used in the sensors. Advantageously, the IMUs mayremain as stable as possible in order to increase an efficiency of thepose detection process. The IMUs may be engineered such that they remainstable up to 50-100 milliseconds. It should be appreciated that someembodiments may utilize an outside pose estimator module (e.g., IMUs maydrift over time) that may enable pose updates to be reported at a rateof 10 to 20 Hz. By keeping the IMUs stable at a reasonable rate, therate of pose updates may be dramatically decreased to 10 to 20 Hz (ascompared to higher frequencies in conventional systems).

If the electromagnetic tracking system can be run at, for example, a 10%duty cycle (e.g., only pinging for ground truth every 100 milliseconds),this would be another way to save power at the AR system. This wouldmean that the electromagnetic tracking system wakes up every 10milliseconds out of every 100 milliseconds to generate a pose estimate.This directly translates to power consumption savings, which may, inturn, affect size, battery life and cost of the AR device.

In one or more embodiments, this reduction in duty cycle may bestrategically utilized by providing two hand-held controllers (notshown) rather than just one. For example, the user may be playing a gamethat requires two totems, etc. Or, in a multi-user game, two users mayhave their own totems/hand-held controllers to play the game. When twocontrollers (e.g., symmetrical controllers for each hand) are usedrather than one, the controllers may operate at offset duty cycles. Thesame concept may also be applied to controllers utilized by twodifferent users playing a multi-player game, for example.

Referring now to FIG. 7, an example flow chart describing theelectromagnetic tracking system in the context of AR devices isdescribed. At 702, a portable (e.g., hand-held) controller emits amagnetic field. At 704, the electromagnetic sensors (placed on headset,belt pack, etc.) detect the magnetic field. At 706, a pose (e.g.,position or orientation) of the headset/belt is determined based on abehavior of the coils/IMUs at the sensors. At 708, the pose informationis conveyed to the computing apparatus (e.g., at the belt pack orheadset). At 710, optionally, a mapping database (e.g., passable worldmodel) may be consulted to correlate the real world coordinates (e.g.,determined for the pose of the headset/belt) with the virtual worldcoordinates. At 712, virtual content may be delivered to the user at theAR headset and displayed to the user (e.g., via the light field displaysdescribed herein). It should be appreciated that the flowchart describedabove is for illustrative purposes only, and should not be read aslimiting.

Advantageously, using an electromagnetic tracking system similar to theone outlined in FIG. 6 enables pose tracking (e.g., head position andorientation, position and orientation of totems, and other controllers).This allows the AR system to project virtual content (based at least inpart on the determined pose) with a higher degree of accuracy, and verylow latency when compared to optical tracking techniques.

Referring to FIG. 8, a system configuration is illustrated whereinfeaturing many sensing components. A head mounted wearable component(58) is shown operatively coupled (68) to a local processing and datamodule (70), such as a belt pack, here using a physical multicore leadwhich also features a control and quick release module (86) as describedbelow in reference to FIGS. 9A-9F. The local processing and data module(70) is operatively coupled (100) to a hand held component (606), hereby a wireless connection such as low power Bluetooth; the hand heldcomponent (606) may also be operatively coupled (94) directly to thehead mounted wearable component (58), such as by a wireless connectionsuch as low power Bluetooth. Generally where IMU data is passed tocoordinate pose detection of various components, a high-frequencyconnection is desirable, such as in the range of hundreds or thousandsof cycles/second or higher; tens of cycles per second may be adequatefor electromagnetic localization sensing, such as by the sensor (604)and transmitter (602) pairings. Also shown is a global coordinate system(10), representative of fixed objects in the real world around the user,such as a wall (8).

Cloud resources (46) also may be operatively coupled (42, 40, 88, 90) tothe local processing and data module (70), to the head mounted wearablecomponent (58), to resources which may be coupled to the wall (8) orother item fixed relative to the global coordinate system (10),respectively. The resources coupled to the wall (8) or having knownpositions and/or orientations relative to the global coordinate system(10) may include a wireless transceiver (114), an electromagneticemitter (602) and/or receiver (604), a beacon or reflector (112)configured to emit or reflect a given type of radiation, such as aninfrared LED beacon, a cellular network transceiver (110), a RADARemitter or detector (108), a LIDAR emitter or detector (106), a GPStransceiver (118), a poster or marker having a known detectable pattern(122), and a camera (124).

The head mounted wearable component (58) features similar components, asillustrated, in addition to lighting emitters (130) configured to assistthe camera (124) detectors, such as infrared emitters (130) for aninfrared camera (124); also featured on the head mounted wearablecomponent (58) are one or more strain gauges (116), which may be fixedlycoupled to the frame or mechanical platform of the head mounted wearablecomponent (58) and configured to determine deflection of such platformin between components such as electromagnetic receiver sensors (604) ordisplay elements (62), wherein it may be valuable to understand ifbending of the platform has occurred, such as at a thinned portion ofthe platform, such as the portion above the nose on the eyeglasses-likeplatform depicted in FIG. 8.

The head mounted wearable component (58) also features a processor (128)and one or more IMUs (102). Each of the components preferably areoperatively coupled to the processor (128). The hand held component(606) and local processing and data module (70) are illustratedfeaturing similar components. As shown in FIG. 8, with so many sensingand connectivity means, such a system is likely to be heavy, powerhungry, large, and relatively expensive. However, for illustrativepurposes, such a system may be utilized to provide a very high level ofconnectivity, system component integration, and position/orientationtracking. For example, with such a configuration, the various mainmobile components (58, 70, 606) may be localized in terms of positionrelative to the global coordinate system using WiFi, GPS, or Cellularsignal triangulation; beacons, electromagnetic tracking (as describedherein), RADAR, and LIDAR systems may provide yet further locationand/or orientation information and feedback. Markers and cameras alsomay be utilized to provide further information regarding relative andabsolute position and orientation. For example, the various cameracomponents (124), such as those shown coupled to the head mountedwearable component (58), may be utilized to capture data which may beutilized in simultaneous localization and mapping protocols, or “SLAM”,to determine where the component (58) is and how it is oriented relativeto other components.

Referring to FIGS. 9A-9F, various aspects of the control and quickrelease module (86) are depicted. Referring to FIG. 9A, two outerhousing components (132, 134) are coupled together using a magneticcoupling configuration which may be enhanced with mechanical latching.Buttons (136) for operation of the associated system may be included,for example, an on/off button (circular button) and up/down volumecontrols (triangular buttons). Opposing ends of the module 86 can beconnected to electrical leads running between the local processing anddata module (70) and the display (62) as shown in FIG. 8.

FIG. 9B illustrates a partial cutaway view with the outer housing (132)removed showing the buttons (136) and the underlying top printed circuitboard (138). Referring to FIG. 9C, with the buttons (136) and underlyingtop printed circuit board (138) removed, a female contact pin array(140) is visible. Referring to FIG. 9D, with an opposite portion ofhousing (134) removed, the lower printed circuit board (142) is visible.With the lower printed circuit board (142) removed, as shown in FIG. 9E,a male contact pin array (144) is visible.

Referring to the cross-sectional view of FIG. 9F, at least one of themale pins or female pins are configured to be spring-loaded such thatthey may be depressed along each pin's longitudinal axis; the pins maybe termed “pogo pins” and generally comprise a highly conductivematerial, such as copper or gold. The conductive material may be platedonto the pins (e.g., immersion or electroplating) and the width of theconductive material may be, e.g., at least 25 μm of gold in some cases.When assembled, the illustrated configuration mates 46 male pins with 46corresponding female pins, and the entire assembly may be quick-releasedecoupled by manually pulling the two housings (132, 134) apart andovercoming a magnetic interface (146) load which may be developed usingnorth and south magnets oriented around the perimeters of the pin arrays(140, 144). In one embodiment, an approximate 2 kg load from compressingthe 46 pogo pins is countered with a closure maintenance force of about4 kg provided by the magnetic interface (146). The pins in the array maybe separated by about 1.3 mm, and the pins may be operatively coupled toconductive lines of various types, such as twisted pairs or othercombinations to support interfaces such as USB 3.0, HDMI 2.0 (fordigital video), and I2S (for digital audio), transition-minimizeddifferential signaling (TMDS) for high speed serial data, generalpurpose input/output (GPIO), and mobile interface (e.g., MIPI)configurations, battery/power connections, and high current analog linesand grounds configured for up to about 4 amps and 5 volts in oneembodiment.

In one embodiment, the magnetic interface (146) is generally rectangularand surrounds the pin arrays (140, 144) and is about 1 mm wide and 4.8mm high. The inner diameter of the rectangular magnet is about 14.6 mm.The magnet surrounding the male pin array (144) may have a firstpolarity (e.g., north), and the magnet surrounding the female pin array(140) may have a second (opposite) polarity (e.g., south). In somecases, each magnet comprises a mixture of north and south polarities,with the opposing magnet having corresponding opposite polarities, toprovide a magnetic attraction to assist holding the housings (132, 134)together.

The pogo pins in the arrays (140, 144) have heights in a range of 4.0 to4.6 mm and diameters in a range of 0.6 to 0.8 mm. Different pins in thearray can have different heights, diameters, and pitches. For example,in one implementation, the pin arrays (140, 144) have a length of about42 to 50 mm, a width of about 7 to 10 mm, and a height of about 5 mm.The pitch of the pin array for USB 2.0 and other signals can be about1.3 mm, and the pitch of the pin array for high speed signals can beabout 2.0 to 2.5 mm.

Referring to FIG. 10, it can be helpful to have a minimizedcomponent/feature set to be able to reduce or minimize the weight orbulk of the various components, and to arrive at a relatively slim headmounted component, for example, such as that (58) featured in FIG. 10.Thus various permutations and combinations of the various componentsshown in FIG. 8 may be utilized.

Example Electromagnetic Sensing Components in an AR System

Referring to FIG. 11A, an electromagnetic sensing coil assembly (604,e.g., 3 individual coils coupled to a housing) is shown coupled to ahead mounted component (58); such a configuration adds additionalgeometry to the overall assembly which may not be desirable. Referringto FIG. 11B, rather than housing the coils in a box or single housing604 as in the configuration of FIG. 11A, the individual coils may beintegrated into the various structures of the head mounted component(58), as shown in FIG. 11B. FIG. 11B shows examples of locations on thehead-mounted display 58 for X-axis coils (148), Y-axis coils (150), andZ-axis coils (152). Thus, the sensing coils can be distributed spatiallyon or about the head-mounted display (58) to provide a desired spatialresolution or accuracy of the localization and/or orientation of thedisplay (58) by the electromagnetic tracking system.

FIGS. 12A-12E illustrate various configurations for using a ferrite core1200 a-1200 e coupled to an electromagnetic sensor to increase fieldsensitivity. FIG. 12A illustrates a solid ferrite core 1200 a in a shapeof a cube, FIG. 12B shows a ferrite core 1200 b configured as aplurality of rectangular disks spaced apart from each other, FIG. 12Cshows a ferrite core 1200 c having a single axis air core, FIG. 12Dshows a ferrite core 1200 d having a three-axis air core, and FIG. 12Eshows a ferrite core 1200 e comprising a plurality of ferrite rods in ahousing (which may be made from plastic). The embodiments 1200 b-1200 eof FIGS. 12B-12E are lighter in weight than the solid core embodiment1200 a of FIG. 12A and may be utilized to save mass. Although shown as acube in FIGS. 12A-12E, the ferrite core can be shaped differently inother embodiments.

Frequency Division Multiplexing, Time Division Multiplexing, and GainControl for EM Tracking Systems

Conventional EM tracking solutions typically employ either a frequencydivision multiplexed (FDM) circuit design or a time division multiplexed(TDM) circuit design. However, an FDM design typically uses more currentand a TDM design typically supports only a limited number of users. Asdescribed further below, a circuit design that merges both the FDM andTDM designs may achieve the benefits of both. Advantages of such adesign can include savings on the area of the printed circuit board(PCB), material costs, number of parts used, and/or current drain ascompared to conventional designs. The design can also allow for multipleusers at improved or optimum performance.

FIG. 13A is a block diagram that schematically illustrates an example ofan EM transmitter (TX) circuit 1302 that is frequency divisionmultiplexed. The EM transmitter circuit can drive three tuned orthogonalcoils in an EM tracking system. The time-varying EM field generated bythe EM TX can be sensed by an EM receiver (e.g., described withreference to FIG. 13B). This circuit uses a master control unit (MCU) tocontrol three different synthesizers at three different radio frequency(RF) frequencies (f1, f2, and f3) whose outputs are filtered (e.g., atbandpass filters (BPF) and optional ferrite beads (FB)) and amplified(e.g., via pre-amplifiers (PA)) and fed to respective X, Y, Z coils. Thecircuit also employs a current sensing control circuit (R-sense andCurrent Ctrl) that ensures that the current into each coil remainsconstant. This circuit also has an RF wireless communication interface(e.g., Bluetooth Low Energy (BLE)) connected to the MCU thatcommunicates with an EM receiver unit described with reference to FIG.13B.

FIG. 13B is a block diagram that schematically illustrates an example ofan EM receiver (RX) circuit 1304 that is frequency division multiplexed.The EM receiver uses three orthogonal coils (X-coil operating atfrequency f1, Y-coil operating at frequency f2, and Z-coil operating atfrequency f3) to receive the time-varying EM signals generated by the EMTX circuit 1302 (see, e.g., FIG. 13A). The three signals areindividually amplified (e.g., via pre-amplifiers (PA)) and filtered(e.g., by bandpass filters (BPF)) in parallel. Optionally, the filteroutput may be further amplified. The amplified output is then fed intoan analog-to-digital (ADC) and the digital signals are processed by adigital signal processor (DSP). The DSP can control the gain of thepre-amplifiers to keep the ADC from saturating. This receiver designalso has a radio frequency (RF) communication link connected to the DSP(or an MCU) that communicates with the EM transmitter (e.g., describedwith reference to FIG. 13B). The RF link can be configured to supportany suitable wireless standard, including Bluetooth Low Energy (BLE).

The EM TX and RX circuits 1302, 1304 shown in FIGS. 13A and 13B (as wellas the TX and RX circuits described below with reference to FIGS.13C-13J) can be used for EM tracking. For example, the EM TX circuit1302 can be used in the EM field emitter 402 and the EM RX circuit 1304used in the EM field sensor 404 described with reference to FIG. 4.Additional embodiments of EM TX and RX circuits will be described thatcan provide advantages such as, e.g., reduced part count, reduced PCBarea, lower material costs, and which may allow for multiple users atoptimum performance.

FIG. 13C is a block diagram that schematically illustrates an example ofan EM transmitter circuit 1302 that is time division multiplexed. Inthis embodiment, the FDM circuit of FIG. 13A has been changed to a timedivision multiplexed circuit. The TDM circuit uses only one path that isdivided into the 3 orthogonal coils. The X, Y, and Z-coils operate,respectively, at frequencies f1, f2, and f3 to generate the time-varyingEM fields that are received by an EM receiver circuit. The TDM circuitrycan operate these coils at respective times t1, t2, and t3 according toa TDM timing protocol (see, e.g., FIGS. 13F and 13G). Automatic GainControl (AGC) can be included in the transmitter circuit (furtherdescribed below with reference to FIGS. 13I and 13J). Each coil can bedynamically frequency tuned to a desired frequency assigned by the MCU.

Dynamic Frequency Tuning

Dynamic frequency tuning can be used to achieve resonance on each coilto obtain increased or maximum current flow in an EM TX circuit. Dynamicfrequency tuning can be used to accommodate multiple users. FIG. 13D isa block diagram that schematically illustrates an example of adynamically tunable circuit 1306. Other embodiments of dynamicallytunable circuits 1306 are described with reference to FIGS. 17D-17G. Inthe circuit shown in FIG. 13D, a transmit coil is represented by aninductor L1. A static capacitor (C2) is in parallel with a tunablecapacitor (C1). In this example, the frequency generated by the coil bytuning the capacitor C1 covers a frequency range from 16 kHz to 30 kHz.FIG. 13E is a graph showing examples of the resonances at variousfrequencies (from 16 kHz to 30 kHz) that can be achieved by dynamicallytuning the circuit 1306 shown in FIG. 13D. In order to accommodatemultiple users, the example dynamic frequency tuning circuit can employone transmit (TX) frequency per user. Examples of the frequencyassignments are shown in Table 1.

TABLE 1 Example Frequency Assignments Start Frequency 16 kHz StopFrequency 30 kHz # of Users 4 # of Frequencies per coil 1 # of TXFrequencies per user 2 Frequency Range 14 kHz Channel Spacing  2 kHzTotal Frequencies Required 8

Time Division Multiplexing

In some embodiments, to achieve time division multiplexing on thetransmitter, synchronization between the transmitter and receivercircuits may be utilized. Two possible scenarios for synchronization arediscussed below.

A first scenario uses synchronization through the RF wireless interface(e.g., BLE) of both the receiver and the transmitter. The wireless RFlink can be used to synchronize the clocks of both the transmitter andthe receiver. After synchronization is achieved, time divisionmultiplexing can be referenced to the on-board real-time clock (RTC).

A second scenario uses synchronization through an electromagnetic pulse.The time of flight of the EM pulse will be significantly shorter thantolerances typically used in the TDM circuit and may be ignored. A TX EMpulse is sent by the transmitter to the receiver, which calculates thetime difference between the receiver clock and the transmitter clock.This time difference is communicated over the RF wireless link as aknown offset or is used to adjust the reference on the wirelessinterface (e.g., BLE) clock.

In some embodiments, one or both of these synchronization scenarios canbe implemented. After synchronization is completed, a time sequence forTDM for the transmitter and receiver can be established. FIG. 13Fillustrates an example of a TDM timing diagram 1308. The TX on theX-coil will stay on for a first time period that allows the X, Y, and Zcoils of the receiver to receive the magnetic flux generated by theX-coil. During the first time period, the TXs on the Y-coil and theZ-coil are substantially off (e.g., the coils are fully off or operatingat a voltage much less (e.g., <10%, <5%, <1%, etc.) than their normaloperating voltage). Following the X-coil transmission, the TX on theY-coil will turn on (and the X-coil will turn substantially off, whilethe Z-coil remains substantially off), and the X, Y, and Z coils of thereceiver will receive the magnetic flux generated by the TX Y-coil.Following the Y-coil transmission, the TX on the Z-coil will turn on(and the Y-coil will turn substantially off, while the X-coil remainssubstantially off), and the X, Y, and Z coils of the receiver willreceive the magnetic flux generated by the TX Z-coil. This timingsequence is then repeated continuously while the EM transmitter isoperating.

The following describes a non-limiting, illustrative example ofaccommodating multiple users. For example, to accommodate up to fourusers with two transmitters each requires eight TX frequencies. It isgenerally advantageous if these frequencies are not duplicated. In suchembodiments, a scan process can be implemented by the EM receiver todetermine if a particular frequency is being used in close proximity.FIG. 13G illustrates an example of scan timing 1310. This scan can bedone by the EM receiver 1304 at initialization as well as periodicallyduring the user's session. The scan can be performed by intentionallyturning off the TX in the transmitter 1302 and cycling through the RX(in the receiver 1304) to measure the existence of unintentionalinterference. If it is determined that there is energy at thatfrequency, then an alternate frequency can be selected. This scan canalso be shortened by monitoring one or two (rather than all three) ofthe three orthogonal coils, because Position and Orientation (PnO) isnot required in that slot.

FIG. 13H is a block diagram that schematically illustrates anotherexample of a receiver 1304 in an EM tracking system. As compared to theexample FDM receiver illustrated in FIG. 13B, a TDM switch has replacedthe individual paths from the three orthogonal coils. The TDM switch canbe controlled by an RF wireless interface (e.g., BLE). The TDM switchcan utilize the timing protocol 1308 illustrated in FIG. 13F.

In various embodiments, the time division multiplexed TX and/or RXcircuits described with reference to FIGS. 13C-13H may provide one ormore of the following advantages. (A) Current Drain and Battery Life. Bytime multiplexing the transmitter and the receiver, the amount ofcurrent used may be lowered. This reduction comes from the fact that thehigh current circuits, such as the transmitter, are no longer beingutilized 100% of the time. The current drain of the system can bereduced to slightly over ⅓ as compared to the FDM circuits shown inFIGS. 13A and 13B. (B) Bill of Materials Cost. The number of componentsused to achieve the same result has been reduced (compared to the FDMcircuits in FIGS. 13A and 13B) in the TDM embodiments described above.Multiplexing the signals through the same path reduces the part countand in this case the cost of the components should also be reduced toslightly over ⅓ compared to the FDM counterparts. (C) PCB Area. Anotherbenefit of the part reduction can be the savings gained in PCB area. Thepart count has reduced by almost ⅔ and so the required space on the PCBis reduced.

Other possible advantages may be reduced mass of the TX and RX circuits.For example, the FDM TX and RX circuits shown in FIGS. 13A and 13Butilize separate filter and amplifier paths for each of the threeorthogonal coils. In contrast, the TDM TX and RX circuits illustrated inFIGS. 13C and 13H share a filter and amplifier path.

In addition to removing sensor housings, and multiplexing to save onhardware overhead, signal-to-noise ratios may be increased by havingmore than one set of electromagnetic sensors, each set being relativelysmall relative to a single larger coil set. Also, the low-side frequencylimits, which generally are needed to have multiple sensing coils inclose proximity, may be improved to facilitate bandwidth requirementimprovements. There generally is a tradeoff with TD multiplexing, inthat multiplexing generally spreads out the reception of RF signals intime, which results in generally noisier signals; thus larger coildiameters may be used for multiplexed systems. For example, where amultiplexed system may utilize a 9 mm-side dimension cubic coil sensorbox, a nonmultiplexed system may only utilize a 7 mm-side dimensioncubic coil box for similar performance; thus there may be tradeoffs inminimizing geometry and mass and selecting between embodiments of FDMand TDM circuits.

Example Automatic Gain Control for an Electromagnetic Tracking System

With reference to FIGS. 13A and 13B, the FDM receiver (FIG. 13B)implements a closed-loop gain control while the FDM transmitter (FIG.13A) does not implement gain control and is left to transmit at itsmaximum output power, regardless of the received level. The gain of thereceiver can be set by the DSP. For example, the received voltages onthe receiver coils are fed directly into the first stage, which has gaincontrol. Large voltages can be determined in the DSP, and the DSP canautomatically adjust the gain of the first stage. Placing the gaincontrol in the receiver may utilize more power in the transmitter, evenwhen it is not needed. Accordingly, it may be advantageous to employautomatic gain control (AGC, sometimes also referred to as adaptive gaincontrol) on the transmitter side (rather than the receiver side), whichmay save space in the receiver system (that would otherwise be used forAGC), thereby allowing for a much smaller and more portable receiver.

FIG. 13I is a block diagram that schematically illustrates an example ofan EM receiver 1304 that does not utilize automatic gain control (AGC).The first stage is no longer an AGC circuit (compare to FIG. 13B), andthe receiver is designed to simply have a constant gain. The level ofthe received voltage on the coils is determined by the DSP, and the DSPprovides that information to the wireless (e.g., BLE) link. This BLElink can provide that information to the transmitter (see FIG. 13J) tocontrol the TX level.

FIG. 13J is a block diagram that schematically illustrates an example ofan EM transmitter 1302 that employs AGC. The EM transmitter 1302 of FIG.13J can communicate with the receiver 1304 of FIG. 13I. The wirelesslink (e.g., BLE) communicates the received voltage level (from the BLElink on the receiver) to the MCU. The amplification stage can haveadjustable gain that is controlled by the MCU. This can allow forcurrent savings on the transmitter when the received voltage required issmall.

Accordingly, the RX and TX circuit examples in FIGS. 13I and 13J employAGC in the EM transmitter 1302 instead of the EM receiver 1304. Thischange from the RX and TX circuit examples in FIGS. 13A and 13B canallow for a smaller RX design as well as a more power efficient designbecause the TX power will be allowed to be reduced when necessary.

Examples of EM Tracking of User Head Pose or Hand Pose

Referring to FIG. 14, in one embodiment, after a user powers up his orher wearable computing system (160), a head mounted component assemblymay capture a combination of IMU and camera data (the camera data beingused, for example, for SLAM analysis, such as at the belt pack processorwhere there may be more raw processing horsepower present) to determineand update head pose (e.g., position or orientation) relative to a realworld global coordinate system (162). The user may also activate ahandheld component to, for example, play an augmented reality game(164), and the handheld component may comprise an electromagnetictransmitter operatively coupled to one or both of the belt pack and headmounted component (166). One or more electromagnetic field coil receiversets (e.g., a set being 3 differently-oriented individual coils) coupledto the head mounted component to capture magnetic flux from thetransmitter, which may be utilized to determine positional ororientational difference (or “delta”), between the head mountedcomponent and handheld component (168). The combination of the headmounted component assisting in determining pose relative to the globalcoordinate system, and the hand held assisting in determining relativelocation and orientation of the handheld relative to the head mountedcomponent, allows the system to generally determine where each componentis relative to the global coordinate system, and thus the user's headpose, and handheld pose may be tracked, preferably at relatively lowlatency, for presentation of augmented reality image features andinteraction using movements and rotations of the handheld component(170).

Referring to FIG. 15, an embodiment is illustrated that is somewhatsimilar to that of FIG. 14, with the exception that the system has manymore sensing devices and configurations available to assist indetermining pose of both the head mounted component (172) and a handheld component (176, 178), such that the user's head pose, and handheldpose may be tracked, preferably at relatively low latency, forpresentation of augmented reality image features and interaction usingmovements and rotations of the handheld component (180).

Example Stereo and Time-of-Flight Depth Sensing

Referring to FIGS. 16A and 16B, various aspects of a configurationsimilar to that of FIG. 8 are shown. The configuration of FIG. 16Adiffers from that of FIG. 8 in that in addition to a LIDAR (106) type ofdepth sensor, the configuration of FIG. 16A features a generic depthcamera or depth sensor (154) for illustrative purposes, which may, forexample, be either a stereo triangulation style depth sensor (such as apassive stereo depth sensor, a texture projection stereo depth sensor,or a structured light stereo depth sensor) or a time or flight styledepth sensor (such as a LIDAR depth sensor or a modulated emission depthsensor); further, the configuration of FIG. 16A has an additionalforward facing “world” camera (124, which may be a grayscale camera,having a sensor capable of 720p range resolution) as well as arelatively high-resolution “picture camera” (156, which may be a fullcolor camera, having a sensor capable of two megapixel or higherresolution, for example). FIG. 16B shows a partial orthogonal view ofthe configuration of FIG. 16A for illustrative purposes, as describedfurther below in reference to FIG. 16B.

Referring back to FIG. 16A and the stereo vs. time-of-flight style depthsensors mentioned above, each of these depth sensor types may beemployed with a wearable computing solution as disclosed herein,although each has various advantages and disadvantages. For example,many depth sensors have challenges with black surfaces and shiny orreflective surfaces. Passive stereo depth sensing is a relativelysimplistic way of getting triangulation for calculating depth with adepth camera or sensor, but it may be challenged if a wide field of view(“FOV”) is required, and may require relatively significant computingresource; further, such a sensor type may have challenges with edgedetection, which may be important for the particular use case at hand.Passive stereo may have challenges with textureless walls, low lightsituations, and repeated patterns. Passive stereo depth sensors areavailable from manufacturers such as Intel and Aquifi. Stereo withtexture projection (also known as “active stereo”) is similar to passivestereo, but a texture projector broadcasts a projection pattern onto theenvironment, and the more texture that is broadcasted, the more accuracyis available in triangulating for depth calculation. Active stereo mayalso require relatively high compute resource, present challenges whenwide FOV is required, and be somewhat suboptimal in detecting edges, butit does address some of the challenges of passive stereo in that it iseffective with textureless walls, is good in low light, and generallydoes not have problems with repeating patterns. Active stereo depthsensors are available from manufacturers such as Intel and Aquifi.

Stereo with structured light, such as the systems developed byPrimesense, Inc. and available under the tradename Kinect, as well asthe systems available from Mantis Vision, Inc., generally utilize asingle camera/projector pairing, and the projector is specialized inthat it is configured to broadcast a pattern of dots that is known apriori. In essence, the system knows the pattern that is broadcasted,and it knows that the variable to be determined is depth. Suchconfigurations may be relatively efficient on compute load, and may bechallenged in wide FOV requirement scenarios as well as scenarios withambient light and patterns broadcasted from other nearby devices, butcan be quite effective and efficient in many scenarios. With modulatedtime of flight type depth sensors, such as those available from PMDTechnologies, A.G. and SoftKinetic Inc., an emitter may be configured tosend out a wave, such as a sine wave, of amplitude modulated light; acamera component, which may be positioned nearby or even overlapping insome configurations, receives a returning signal on each of the pixelsof the camera component and depth mapping may be determined/calculated.Such configurations may be relatively compact in geometry, high inaccuracy, and low in compute load, but may be challenged in terms ofimage resolution (such as at edges of objects), multi-path errors (suchas wherein the sensor is aimed at a reflective or shiny corner and thedetector ends up receiving more than one return path, such that there issome depth detection aliasing.

Direct time of flight sensors, which also may be referred to as theaforementioned LIDAR, are available from suppliers such as LuminAR andAdvanced Scientific Concepts, Inc. With these time of flightconfigurations, generally a pulse of light (such as a picosecond,nanosecond, or femtosecond long pulse of light) is sent out to bathe theworld oriented around it with this light ping; then each pixel on acamera sensor waits for that pulse to return, and knowing the speed oflight, the distance at each pixel may be calculated. Such configurationsmay have many of the advantages of modulated time of flight sensorconfigurations (no baseline, relatively wide FOV, high accuracy,relatively low compute load, etc.) and also relatively high framerates,such as into the tens of thousands of Hertz. They may also be relativelyexpensive, have relatively low resolution, be sensitive to bright light,and susceptible to multi-path errors; they may also be relatively largeand heavy.

Referring to FIG. 16B, a partial top view is shown for illustrativepurposes featuring a user's eyes (12) as well as cameras (14, such asinfrared cameras) with fields of view (28, 30) and light or radiationsources (16, such as infrared) directed toward the eyes (12) tofacilitate eye tracking, observation, and/or image capture. The threeoutward-facing world-capturing cameras (124) are shown with their FOVs(18, 20, 22), as is the depth camera (154) and its FOV (24), and thepicture camera (156) and its FOV (26). The depth information garneredfrom the depth camera (154) may be bolstered by using the overlappingFOVs and data from the other forward-facing cameras. For example, thesystem may end up with something like a sub-VGA image from the depthsensor (154), a 720p image from the world cameras (124), andoccasionally a 2 megapixel color image from the picture camera (156).Such a configuration has four cameras sharing common FOV, two of themwith heterogeneous visible spectrum images, one with color, and thethird one with relatively low-resolution depth. The system may beconfigured to do a segmentation in the grayscale and color images, fusethose two and make a relatively high-resolution image from them, getsome stereo correspondences, use the depth sensor to provide hypothesesabout stereo depth, and use stereo correspondences to get a more refineddepth map, which may be significantly better than what was availablefrom the depth sensor only. Such processes may be run on local mobileprocessing hardware, or can run using cloud computing resources, perhapsalong with the data from others in the area (such as two people sittingacross a table from each other nearby), and end up with quite a refinedmapping. In another embodiment, all of the above sensors may be combinedinto one integrated sensor to accomplish such functionality.

Example Dynamic Tuning of a Transmission Coil for EM Tracking

Referring to FIGS. 17A-17G, aspects of a dynamic transmission coiltuning configuration are shown for electromagnetic tracking, tofacilitate the transmission coil to operate optimally at multiplefrequencies per orthogonal axis, which allows for multiple users tooperate on the same system. Typically an electromagnetic trackingtransmitter will be designed to operate at fixed frequencies perorthogonal axis. With such an approach, each transmission coil is tunedwith a static series capacitance that creates resonance only at thefrequency of operation. Such resonance allows for the maximum possiblecurrent flow through the coil which, in turn, maximizes the magneticflux generated. FIG. 17A illustrates a typical resonant circuit 1305used to create resonance at a fixed operation frequency. Inductor “L”represents a single axis transmission coil having an inductance of 1 mH,and with a capacitance set to 52 nF, resonance is created at 22 kHz, asshown in FIG. 17B. FIG. 17C shows the current through the circuit 1305of FIG. 17A plotted versus frequency, and it may be seen that thecurrent is maximum at the resonant frequency. If this system is expectedto operate at any other frequency, the operating circuit will not be atthe possible maximum current (which occurs at the resonant frequency of22 kHz).

FIG. 17D illustrates an embodiment of a dynamically tunableconfiguration for the transmitter circuit 1306 of a transmitter 1302 ofan electromagnetic tracking system. The example circuit 1306 shown inFIG. 17D may be used in embodiments of the EM field emitter 402, 602,1302 described herein. The circuit in FIG. 17D includes an oscillatingvoltage source 1702, a transmit (TX) coil, a high voltage (HV)capacitor, and a plurality of low voltage (LV) capacitors in a capacitorbank 1704 that can be selected to provide the tuning for a desiredresonance frequency. The dynamic frequency tuning may be set to achieveresonance on the coil (at desired, dynamically adjustable frequencies)to get maximum current flow. Another example of a dynamically tunablecircuit 1306 is shown in FIG. 17E, where a tunable capacitor 1706 (“C4”)may be tuned to produce resonance at different frequencies, as shown inthe simulated data illustrated in FIG. 17F. Tuning the tunable capacitorcan include switching among a plurality of different capacitors asschematically illustrated in the circuit shown in FIG. 17D. As shown inthe embodiment of FIG. 17E, one of the orthogonal coils of anelectromagnetic tracker is simulated as an inductor “L” and a staticcapacitor (“C5”) is a fixed high voltage capacitor. This high voltagecapacitor will see the higher voltages due to the resonance, and so itspackage size generally will be larger. Capacitor C4 will be thecapacitor which is dynamically switched with different values, and canthus see a lower maximum voltage and generally be a smaller geometricpackage to save placement space. Inductor L3 can also be utilized tofine tune the resonant frequency.

FIG. 17F illustrates examples of the resonances that may be achieved bythe circuit 1306 of FIG. 17E. In FIG. 17F, the higher curves (248) showthe voltage Vmid−Vout across the capacitor C5, and the lower curves(250) show the voltage Vout across the capacitor C4. As the capacitanceof C4 is varied, the resonance frequency is changed (between about 22kHz and 30 kHz in this example), and it is notable that the voltageacross C5 (Vmid−Vout; curves 248) is higher than that across C4 (Vout;curves 250). This generally will allow for a smaller package part on C4since multiples of this capacitor generally will be used in the system,e.g., one capacitor per resonant frequency of operation (see, e.g., themultiple LV capacitors in the capacitor bank 1704 shown in FIG. 17D).FIG. 17G is a plot of current versus frequency that illustrates that themaximum current achieved follows the resonance regardless of the voltageacross the capacitors. Accordingly, embodiments of the dynamicallytunable circuit can provide increased or maximum current in thetransmitter coil across multiple frequencies allowing for improved oroptimized performance for multiple users of a single EM tracking system.

Example Audio Noise Canceling for an EM Tracking System

Audio speakers (or any external magnet) can create a magnetic field thatcan unintentionally interfere with the magnetic field created by the EMfield emitter of an EM tracking system. Such interference can degradethe accuracy or reliability of the location estimation provided by theEM tracking system.

As AR devices evolve, they become more complicated and integrate moretechnologies that have to coexist and perform independently. EM trackingsystems rely on reception (by the EM sensor) of minute changes in amagnetic flux (generated by the EM field emitter) to determine a 3-Dposition of the EM sensor (and thereby the 3-D position of the object towhich the sensor is attached or incorporated). Audio speakers thatreside close to the EM tracking sensor coils can emit a magnetic fluxthat can interfere with the EM tracking system's ability to compute atrue position.

Referring to FIGS. 18A-18C, an electromagnetic tracking system may bebounded to work below about 30 kHz, which is slightly higher than theaudible range for human hearing. FIG. 18A shows a configuration where anaudio speaker 1820 is in close proximity to an EM sensor 604. The audiospeaker 1820 is driven by a time-varying voltage source 1822 and anamplifier 1824. The magnetic field of the speaker 1820 can causeunintentional magnetic interference to the EM tracking system, becausethe speaker generates noise in the magnetic field sensed by the coils ofthe EM sensor 604. In some implementations, the distance between theaudio speaker 1820 and the EM sensor 604 can be increased to reduce thereceived interference. But because the magnetic flux from the speakerdecays by the cube of the distance from the sensor (1/r³), there will bea point where large distances provide very little decay in theinterference. An audio speaker (e.g., speaker 66 shown in FIGS. 2A-2D)will commonly be used in AR devices to provide an audio experience tothe wearer of the AR device; therefore, it may be common that an audiospeaker is relatively near to an EM sensor also disposed on the ARdevice (see, e.g., the EM sensor 604 disposed near the speaker 66 in theexample wearable display device 58 shown in FIG. 11A). The magneticfield from the audio speaker can interfere with the EM field sensed bythe EM sensor of the EM tracking system.

Referring to FIG. 18A, there may be some audio systems which createnoise in the usable frequencies for such electromagnetic trackingsystems. Further, audio speakers typically have magnetic fields and oneor more coils, which also may interfere with electromagnetic trackingsystems. Referring to FIG. 18B, a block diagram is shown for an exampleof a noise cancelling system 1830 for an electromagnetic trackingsystem. Since the unintentional EM interference is a known entity(because the signal supplied by the voltage source 1822 to the audiospeaker 1820 is known or can be measured), this knowledge can be used tocancel the EM interference from the audio speaker 1820 and improveperformance of the EM tracking system. In other words, the audio signalgenerated by the system may be utilized to eliminate the magneticinterference from the speaker that is received by the coil of the EMsensor 604. As schematically shown in FIG. 18B, the noise cancellingcircuit 1830 may be configured to accept the corrupted signals 1850 afrom the EM sensor 604 as well as the signal 1850 b from the audiosystem. The noise cancelling system can combine the signals 1850 a, 1850b to cancel out the interference received from the audio speaker 1820and to provide an uncorrupted sensor signal 1850 c.

FIG. 18C is a plot showing an illustrative, non-limiting example of howthe audio signal 1850 b can be inverted and added to the corruptedsensor signal 1850 a cancel the interference and to provide thesubstantially uncorrupted sensor signal 1850 c. The top plot, V(noise),is the noise signal 1850 b added to the EM tracking system by the audiospeaker 1820. The bottom plot, V(cancel), is the inverted audio signal(e.g., −V(noise)), when these are added together the effect is no noisedegradation from the audio. In other words, the noise canceling systemreceives a corrupted signal 1850 a that is the sum of the true EM sensorsignal, V(sensor) representing the signal from the EM transmitter coils,and the noise signal: V(sensor)+V(noise). By adding the inverted audiosignal, −V(noise), to the corrupted signal 1850 a, the uncorruptedsignal, V(sensor) 1850 c, is recovered. The uncorrupted signal 1850 creflects the response of the sensor 604 as if the audio speaker 604 werenot present and therefore reflects the EM transmitter fields at theposition of the sensor 604. Equivalently, the noise signal 1850 b can besubtracted from the corrupted signal 1850 a to recover the uncorruptedsignal, V(sensor) 1850 c. The noise cancellation can result in cancelingsubstantially all (e.g., >80%, >90%, >95%, or more) of the noise signal(e.g., from the audio speaker). This noise cancellation technique is notlimited to cancellation of just audio speaker noise but can be appliedto other sources of noise interference to the EM sensor signal if ameasurement (or estimate) of the noise signal can be determined (so thatit can then be removed from the EM sensor signal as described above).

FIG. 18D is a flowchart that shows an example method 1800 for cancelinginterference received by an EM sensor in an EM tracking system. Themethod 1800 can be performed by a hardware processor in the AR devicesuch as, e.g., the local processing and data module 70, or by a hardwareprocessor in the EM tracking system. At block 1802, the method receivesa noisy signal from an electromagnetic sensor. As described above, thenoisy signal can be caused by interference from a nearby audio speakerthat generates electromagnetic interference. At block 1804, the methodreceives a signal from the source of the EM interference. For example,the signal can be the signal 1850 b used to drive the audio speaker(see, e.g., FIG. 18B). At block 1806, the noisy signal and theinterference signal are combined to obtain a de-noised EM signal. Forexample, the interference signal can be inverted and added to the noisysignal or the interference signal can be subtracted from the noisysignal. At block 1808, the de-noised signal can be used to determine thelocation of the EM sensor. The location obtained using the de-noisedsignal (as compared to using the noisy signal) is more accurate andreliable.

Accordingly, the foregoing provides a method to remove the unintentionalnoise created by an audio speaker in proximity to an EM tracker sensor.This method employs a noise cancelling method that uses the knowninformation about the audio to remove it from the EM tracking signal.This system may be used when sufficient physical separation of the audiospeaker and the EM sensor coil cannot be achieved (so that theinterference is sufficiently low). Although in the foregoing, theinterference noise has been described as generated by an audio speaker,this is for illustration and is not a limitation. Embodiments of theforegoing can be applied to any interference signal that can bemeasured, and then subtracted from the corrupted sensor signal.

Example Calibration of Vision Systems

Referring to FIG. 19, in one embodiment a known pattern 1900 (such as acircular pattern) of lights or other emitters may be utilized to assistin calibration of vision systems. For example, the circular pattern maybe utilized as a fiducial; as a camera or other capture device withknown orientation captures the shape of the pattern while the objectcoupled to the pattern is reoriented, the orientation of the object,such as a hand held totem device 606, may be determined; suchorientation may be compared with that which comes from an associated IMUon the object (e.g., the totem) for error determination and use incalibration. With further reference to FIG. 19, the pattern of lights1900 may be produced by light emitters (e.g., a plurality of LEDs) on ahand-held totem 606 (schematically represented as a cylinder in FIG.19). As shown in FIG. 19, when the totem is viewed head-on by a cameraon the AR headset 58, the pattern of lights 1900 appears circular. Whenthe totem 606 is tilted in other orientations, the pattern 1900 appearselliptical. The pattern of lights 1900 can be identified using computervision techniques and the orientation of the totem 606 can bedetermined.

In various implementations, the augmented reality device can include acomputer vision system configured to implement one or more computervision techniques to identify the pattern of lights (or perform othercomputer vision procedures used or described herein). Non-limitingexamples of computer vision techniques include: Scale-invariant featuretransform (SIFT), speeded up robust features (SURF), oriented FAST androtated BRIEF (ORB), binary robust invariant scalable keypoints (BRISK),fast retina keypoint (FREAK), Viola-Jones algorithm, Eigenfacesapproach, Lucas-Kanade algorithm, Horn-Schunk algorithm, Mean-shiftalgorithm, visual simultaneous location and mapping (vSLAM) techniques,a sequential Bayesian estimator (e.g., Kalman filter, extended Kalmanfilter, etc.), bundle adjustment, Adaptive thresholding (and otherthresholding techniques), Iterative Closest Point (ICP), Semi GlobalMatching (SGM), Semi Global Block Matching (SGBM), Feature PointHistograms, various machine learning algorithms (such as e.g., supportvector machine, k-nearest neighbors algorithm, Naive Bayes, neuralnetwork (including convolutional or deep neural networks), or othersupervised/unsupervised models, etc.), and so forth.

Example Circuits for Subsystems of Wearable Display Devices

Referring to FIGS. 20A-20C, a configuration is shown with a summingamplifier 2002 to simplify circuitry between two subsystems orcomponents of a wearable computing configuration such as a head mountedcomponent and a belt-pack component. With a conventional configuration,each of the coils 2004 (on the left of FIG. 20A) of an electromagnetictracking sensor 604 is associated with an amplifier 2006, and threedistinct amplified signals can be sent through a summing amplifier 2002and the cabling to the other component (e.g., processing circuitry asshown in FIG. 20B). In the illustrated embodiment, the three distinctamplified signals may be directed to the summing amplifier 2002, whichproduces one amplified signal that is directed down an advantageouslysimplified cable 2008, and each signal may be at a different frequency.The summing amplifier 2002 may be configured to amplify all threesignals received by the amplifier; then (as illustrated in FIG. 20B) thereceiving digital signal processor, after analog-to-digital conversion,separates the signals at the other end. Gain control may be used. FIG.20C illustrates a filter for each frequency (F1, F2, and F3)—so thesignals may be separated back out at such stage. The three signals maybe analyzed by a computational algorithm (e.g., to determine sensorpose) and the position or orientation result can be used by the ARsystem (e.g., to properly display virtual content to the user based onthe user's instantaneous head pose).

Example EM Tracking System Updating

Referring to FIG. 21, electromagnetic (“EM”) tracking updating can berelatively “expensive” in terms of power for a portable system, and maynot be capable of very high frequency updating. In a “sensor fusion”configuration, more frequently updated localization information fromanother sensor such as an IMU may be combined, along with data fromanother sensor, such as an optical sensor (e.g., a camera or a depthcamera), which may or may not be at a relatively high frequency; the netof fusing all of these inputs places a lower demand upon the EM systemand provides for quicker updating.

Referring back to FIG. 11B, a distributed sensor coil configuration wasshown for the AR device 58. Referring to FIG. 22A, an AR device 58 witha single electromagnetic sensor device (604), such as a housingcontaining three orthogonal sensing coils, one for each direction of X,Y, Z, may be coupled to the wearable component (58) for 6 degree offreedom tracking, as described above. Also as noted above, such a devicemay be dis-integrated, with the three sub-portions (e.g., coils)attached at different locations of the wearable component (58), as shownin FIGS. 22B and 22C. Referring to FIG. 22C, to provide further designalternatives, each individual sensor coil may be replaced with a groupof similarly oriented coils, such that the overall magnetic flux for anygiven orthogonal direction is captured by the group (148, 150, 152)rather than by a single coil for each orthogonal direction. In otherwords, rather than one coil for each orthogonal direction, a group ofsmaller coils may be utilized and their signals aggregated to form thesignal for that orthogonal direction. In another embodiment wherein aparticular system component, such as a head mounted component (58)features two or more electromagnetic coil sensor sets, the system may beconfigured to selectively utilize the sensor and emitter pairing thatare closest to each other (e.g., within 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, or10 cm) to improve or optimize the performance of the system.

Examples of Recalibrating a Wearable Display System

Referring to FIGS. 23A-23C, it may be useful to recalibrate a wearablecomputing system such as those discussed herein, and in one embodiment,acoustic (e.g., ultrasonic) signals generated at the transmitter, alongwith an acoustic sensor (e.g., microphone) at the receiver and acoustictime of flight calculation, may be utilized to determine soundpropagation delay between the transmitter and receiver and therebydistance between the transmitter and receiver (since the speed of soundis known). FIG. 23A shows that in one embodiment, three coils on thetransmitter are energized with a burst of sinewaves, and at the sametime an ultrasonic transducer may be energized with a burst ofsinewaves, preferably of the same frequency as one of the coils. FIG.23B illustrates that an EM receiver may be configured to receive thethree EM waves using X, Y, Z sensor coils, and the acoustic, ultrasonicwave using a microphone (MIC). Total distance may be calculated from theamplitude of the three EM signals. Time of flight (sound propagationdelay time 2300) may be calculated by comparing the timing of theacoustic (microphone) response 2302 with the response of the EM coils2304 (see, e.g., FIG. 23C). This may be used to also calculate distance.Comparing the electromagnetically calculated distance with the acousticdelay time 2300 can be used to calibrate the EM TX or RX circuits (e.g.,by correction factors).

Referring to FIG. 24A, in another embodiment, in an augmented realitysystem featuring a camera, the distance may be calculated by measuringthe size in pixels of a known-size alignment feature (depicted as anarrow in FIG. 24A) on another device such as a handheld controller(e.g., the controller 606).

Referring to FIG. 24B, in another embodiment, in an augmented realitysystem featuring a depth sensor, such as an infrared (“IR”) depthsensor, the distance may be calculated by such depth sensor and reporteddirectly to the controller.

Referring to FIGS. 24C and 24D, once the total distance is known, eitherthe camera or the depth sensor can be used to determine position inspace. The augmented reality system may be configured to project one ormore virtual alignment targets to the user. The user may align thecontroller to the targets, and the system can calculate position fromboth the EM response, and from the direction of the virtual targets plusthe previously calculated distance. Roll angle calibration may be doneby aligning a known feature on the controller with a virtual targetprojected to the user; yaw and pitch angle may be calibrated bypresenting a virtual target to the user and having the user align twofeatures on the controller with the target (much like sighting a rifle).

Referring to FIGS. 25A and 25B, there may be an inherent ambiguityassociated with EM tracking systems: a receiver would generate a similarresponse in two diagonally opposed locations around the transmitter. Forexample, FIG. 25A shows a handheld device 606 and a ghost device 606 athat generates a similar response. Such a challenge is particularlyrelevant in systems wherein both the transmitter and receiver may bemobile relative to each other.

In one embodiment, the system may use an IMU sensor to determine if theuser is on the plus or the negative side of a reference (e.g., symmetry)axis. In an embodiment such as those described above which feature worldcameras and a depth camera, the system can use that information todetect whether a handheld component (e.g., handheld 2500 in FIG. 25B) isin the positive side or negative side of the reference axis; if thehandheld 2500 is outside of the field of view of the camera and/or depthsensor, the system may be configured to decide (or the user may decide)that the handheld component 2500 is in the 180-degree zone directly inback of the user, for example, at the ghost position 2500 a as shown inFIG. 25B.

Additional Aspects and Advantages

In a first aspect, a head-mounted display system comprises a displaypositionable in front of eyes of a wearer; an electromagnetic (EM) fieldemitter configured to generate a magnetic field having a frequency; anEM sensor configured to sense the magnetic field at the frequency; and aprocessor programmed to: receive signals from the EM sensor indicativeof a sensed magnetic field; and analyze the received signals todetermine a position or an orientation of the EM sensor.

In a second aspect, the head-mounted display system of aspect 1, whereinthe display comprises a light field display.

In a third aspect, the head-mounted display system of aspect 1 or aspect2, wherein the EM field emitter comprises a time division multiplexed(TDM) circuit.

In a fourth aspect, the head-mounted display system of aspect 3, whereinthe TDM circuit comprises a single amplifier circuit that is TDMswitched to each of a plurality of radio frequency (RF) transmittercoils.

In a fifth aspect, the head-mounted display system of aspect 3 or aspect4, wherein the EM field emitter is configured to dynamically tune thefrequency.

In a sixth aspect, the head-mounted display system of aspect 5, whereinto dynamically tune the frequency, the EM field emitter is configured tochange a capacitance of a capacitor or to select among a plurality ofcapacitors in a capacitor bank.

In a seventh aspect, the head-mounted display system of any one ofaspects 3 to 6, wherein the EM field emitter comprises a first wirelessinterface, the EM sensor comprises a second wireless interface and a TDMcircuit, and the EM field emitter and the EM sensor are configured to:establish a wireless link between the first wireless interface and thesecond wireless interface; and synchronize over the wireless link.

In an eighth aspect, the head-mounted display system of any one ofaspects 3 to 7, wherein the EM field emitter is configured to transmitan EM pulse to the EM sensor, and the EM field emitter or the EM sensoris configured to determine a timing difference between an EM fieldemitter clock and an EM sensor clock.

In a ninth aspect, the head-mounted display system of aspect 7 or aspect8, wherein the EM field emitter comprises a first coil and a secondcoil, and the EM field emitter is configured to apply a TDM timingprotocol in which: the first coil transmits during a first time period,while the second coil does not substantially transmit during the firsttime period; and the second coil transmits during a second time periodthat is different from the first time period, while the first coil doesnot substantially transmit during the second time period.

In a 10th aspect, the head-mounted display system of any one of aspects7 to 9, wherein the EM sensor is configured to: scan for unintentionalRF interference at the frequency during a third time period; and inresponse to a determination of the presence of unintentional RFinterference at the frequency, switch to an alternate frequency that isdifferent from the frequency.

In an 11th aspect, the head-mounted display system of aspect 10, whereinthe EM field emitter is configured to substantially stop transmittingduring the third time period.

In a 12th aspect, the head-mounted display system of any one of aspects1 to 11, wherein the EM field emitter comprises an automatic gaincontrol (AGC) circuit.

In a 13th aspect, the head-mounted display system of aspect 12, whereinthe EM sensor does not include an AGC circuit.

In a 14th aspect, the head-mounted display system of aspect 12 or aspect13, wherein the AGC circuit of the EM field emitter is configured to:receive a voltage level for a coil in the EM sensor; and adjust a gainfor an amplification stage of the EM field emitter based at least partlyon the received voltage level.

In a 15th aspect, the head-mounted display system of any one of aspects1 to 14, wherein the head-mounted display system further comprises anaudio speaker and the EM sensor comprises a noise canceling circuit.

In a 16th aspect, the head-mounted display system of aspect 15, whereinthe noise canceling circuit is configured to: receive a first signalfrom the EM sensor; receive a second signal from the audio speaker;combine the first signal and the second signal to provide anoise-canceled signal.

In a 17th aspect, the head-mounted display system of aspect 16, whereinto combine the first signal and the second signal, the noise cancelingcircuit is configured to: (a) invert the second signal and add theinverted second signal to the first signal or (b) subtract the secondsignal from the first signal.

In an 18th aspect, the head-mounted display system of any one of aspects1 to 17, further comprising a user-input totem, the user-input totemcomprising the EM field emitter.

In a 19th aspect, the electromagnetic (EM) tracking system comprises: anEM field emitter comprising a first transmitter coil configured togenerate a first magnetic field having a first frequency, a secondtransmitter coil configured to generate a second magnetic field having asecond frequency, and a third transmitter coil configured to generate athird magnetic field having a third frequency, the EM field emittercomprising a first time division multiplexed (TDM) circuit configured toswitch power among the first transmitter coil, the second transmittercoil, and the third transmitter coil.

In a 20th aspect, the EM tracking system of aspect 19, wherein the firsttransmitter coil, the second transmitter coil, and the third transmittercoil are disposed along with mutually orthogonal axes.

In a 21st aspect, the EM tracking system of aspect 19 or aspect 20,wherein the EM field emitter is configured to dynamically tune the firstfrequency, the second frequency, or the third frequency.

In a 22nd aspect, the EM tracking system of any one of aspects 19 to 21,wherein to dynamically tune the first, the second, or the thirdfrequency, the EM field emitter is configured to change a capacitance ofa capacitor or to select among a plurality of capacitors in a capacitorbank.

In a 23rd aspect, the EM tracking system of any one of aspects 19 to 22,wherein the EM field emitter is configured with an automatic gaincontrol (AGC) circuit.

In a 24th aspect, the EM tracking system of aspect 23, wherein the AGCcircuit comprises a control loop between a digital signal processor(DSP) and an amplification stage.

In the 25th aspect, the EM tracking system of aspect 23 or aspect 24,wherein the EM field emitter is configured to: receive a voltage levelfor a coil in an EM sensor; and adjust a gain for an amplification stageof the EM field emitter based at least partly on the received voltagelevel.

In the 26th aspect, the EM tracking system of any one of aspects 19 to25, further comprising an EM sensor comprising: a first receiver coilconfigured to sense the first magnetic field having the first frequency,a second receiver coil configured to sense the second magnetic fieldhaving the second frequency, and a third receiver coil configured tosense the third magnetic field having the third frequency, the EM fieldsensor comprising a second time division multiplexed (TDM) circuitconfigured to switch power among the first receiver coil, the secondreceiver coil, and the third receiver coil.

In the 27th aspect, the EM tracking system of aspect 26, wherein the EMtracking system is configured to synchronize the EM field emitter andthe EM sensor via a wireless link between the EM field emitter and theEM sensor.

In the 28th aspect, the EM tracking system of aspect 27, wherein: the EMfield emitter is configured to transmit an EM pulse to the EM sensor;and the EM field emitter or the EM sensor is configured to determine atiming difference between an EM field emitter clock and an EM sensorclock.

In a 29th aspect, the EM tracking system of any one of aspects 26 to 28,wherein during a first time period: the first transmitter coil isconfigured to generate the first magnetic field having the firstfrequency during which the second transmitter coil and the thirdtransmitter coil do not substantially transmit the respective secondmagnetic field and third magnetic field; and the first receiver coil,the second receiver coil, and the third receiver coil of the EM sensorare configured to be sequentially activated.

In a 30th aspect, the EM tracking system of aspect 29, wherein during asecond time period following the first time period: the secondtransmitter coil is configured to generate the second magnetic fieldhaving the second frequency during which the first transmitter coil andthe third transmitter coil are configured to not substantially transmitthe respective first magnetic field and third magnetic field; and thefirst receiver coil, the second receiver coil, and the third receivercoil of the EM sensor are configured to be sequentially activated.

The 31st aspect, the EM tracking system of any one of aspects 26 to 30,wherein the EM sensor is configured to scan for frequencies in use.

In a 32nd aspect, the EM tracking system of aspect 31, wherein during athird time period: the first transmitter coil is configured to notsubstantially transmit the first magnetic field; and the first receivercoil is configured to be activated to measure presence of interferenceat the first frequency.

In a 33rd aspect, the EM tracking system of aspect 32, wherein inresponse to detection of interference at the first frequency, the EMtracking system is configured to change the first frequency to adifferent frequency.

In a 34th aspect, the EM tracking system of any one of aspects 26 to 33,wherein the EM sensor is configured to: receive an interference signalrepresentative of a source of magnetic interference; at least partiallycancel the interference signal to output a sensor signal that issubstantially free from the source of magnetic interference.

In a 35th aspect, an electromagnetic (EM) tracking system comprises: anEM field emitter comprising an automatic gain control (AGC) circuit anda transmitter coil; and an EM sensor without an AGC circuit, the EMsensor comprising a sensor coil.

In a 36th aspect, the EM tracking system of aspect 35, wherein: the EMsensor is configured to wirelessly communicate a sensor coil signallevel to the EM field emitter; and the EM field emitter is configured toadjust a gain of the transmitter coil based at least in part on thesensor coil signal level.

In a 37th aspect, the EM tracking system of aspect 35 or aspect 36,wherein the EM field emitter is configured to dynamically adjust a radiofrequency emitted by the transmitter coil.

In a 38th aspect, the EM tracking system of any one of aspects 35 to 37,wherein the EM field emitter and the EM sensor are configured to operateusing time division multiplexing.

In a 39th aspect, the EM tracking system of any one of aspects 35 to 38,wherein the EM sensor is configured to: receive an interference signalrepresentative of a source of magnetic interference; at least partiallycancel the interference signal to output a sensor signal that issubstantially free from the source of magnetic interference.

In a 40th aspect, a head-mounted augmented reality (AR) display devicecomprising the EM tracking system of any one of aspects 35 to 39.

In a 41st aspect, the head-mounted AR display device of aspect 40,wherein the EM sensor is disposed on a frame of the AR display device.

In a 42nd aspect, the head-mounted AR display device of aspect 40 oraspect 41, wherein the EM field emitter is disposed in a handheld,user-input totem.

In a 43rd aspect, an augmented reality display system comprises adisplay configured to project virtual images to eyes of a wearer; aframe configured to mount the display in front of the eyes of thewearer; an electromagnetic (EM) field emitter configured to generate amagnetic field; an EM sensor configured to sense the magnetic field,wherein one of the EM field emitter or the EM sensor is mechanicallycoupled to the frame and the other of the EM field emitter or the EMsensor is mechanically coupled to a component of the augmented realitydisplay system that is independently movable relative to the frame; anda hardware processor programmed to: receive signals from the EM sensorindicative of a sensed magnetic field; and analyze the received signalsto determine a position or an orientation of the EM sensor.

In a 44th aspect, the augmented reality display system of aspect 43,wherein the display comprises a light field display.

In a 45th aspect, the augmented reality display system of aspect 43 oraspect 44, wherein: the component comprises a user-input totem or a beltpack, the EM sensor is mechanically coupled to the frame, and the EMfield emitter is mechanically coupled to the user-input totem or thebelt pack.

In a 46th aspect, the augmented reality display system of any one ofaspects 43 to 45, further comprising: an audio speaker, wherein theaugmented reality display system comprises a noise canceling circuitconfigured to cancel magnetic interference in the sensed magnetic fieldgenerated by the audio speaker. The audio speaker may be mechanicallycoupled to the frame.

In a 47th aspect, the augmented reality display system of aspect 46,wherein the noise canceling circuit is configured to: receive a firstsignal from the EM sensor; receive a second signal from the audiospeaker; combine the first signal and the second signal to provide anoise-canceled signal.

In a 48th aspect, the augmented reality display system of aspect 47,wherein to combine the first signal and the second signal, the noisecanceling circuit is configured to: (a) invert the second signal and addthe inverted second signal to the first signal or (b) subtract thesecond signal from the first signal.

In a 49th aspect, the augmented reality display system of any one ofaspects 43 to 48, wherein the EM field emitter comprises: a firsttransmitter coil configured to generate a first magnetic field having afirst frequency; and a second transmitter coil configured to generate asecond magnetic field having a second frequency; and a time divisionmultiplexed (TDM) circuit configured to switch power respectivelybetween the first transmitter coil and the second transmitter coil.

In a 50th aspect, the augmented reality display system of aspect 49,wherein the TDM circuit comprises a single amplifier circuit that is TDMswitched to each of the first and the second transmitter coils.

In a 51st aspect, the augmented reality display system of aspect 49 oraspect 50, wherein the first transmitter coil and the second transmittercoil are disposed along mutually orthogonal axes.

In a 52nd aspect, the augmented reality display system of any one ofaspects 43 to 51, wherein the EM field emitter is configured todynamically tune the first frequency or the second frequency.

In a 53rd aspect, the augmented reality display system of aspect 52,wherein to dynamically tune the first frequency or the second frequency,the EM field emitter is configured to change a capacitance of acapacitor or to select among a plurality of capacitors in a capacitorbank.

In a 54th aspect, the augmented reality display system of any one ofaspects 43 to 53, wherein the EM field emitter comprises a firstwireless interface, the EM sensor comprises a second wireless interfaceand a second TDM circuit, and the EM field emitter and the EM sensor areconfigured to: establish a wireless link between the first wirelessinterface and the second wireless interface; and synchronize timing ofan EM field emitter clock with an EM sensor clock over the wirelesslink.

In a 55th aspect, the augmented reality display system of any one ofaspects 43 to 54, wherein the EM field emitter is configured to transmitan EM pulse to the EM sensor, and the EM field emitter or the EM sensoris configured to determine a timing difference between an EM fieldemitter clock and an EM sensor clock. In another aspect, the AR displaysystem of any one of aspects 43 to 54 may be configured such that the EMfield emitter comprises an acoustic generator and the EM sensorcomprises an acoustic sensor. The AR display system may be configured todetermine a time of flight of a first distance between the emitter andthe sensor based at least in part on a measured delay between anacoustic signal and an electromagnetic signal. The AR display system maybe further configured to determine a second distance between the emitterand the sensor based at least in part on an amplitude of theelectromagnetic signals. The AR display system may be further configuredto calibrate the system based at least in part on a comparison of thefirst distance and the second distance.

In a 56th aspect, the augmented reality display system of any one ofaspects 49 to 55, wherein the EM field emitter is configured to apply aTDM timing protocol in which: the first transmitter coil transmitsduring a first time period, while the second transmitter coil does notsubstantially transmit during the first time period; and the secondtransmitter coil transmits during a second time period that is differentfrom the first time period, while the first transmitter coil does notsubstantially transmit during the second time period.

In a 57th aspect, the augmented reality display system of any one ofaspects 43 to 56, wherein the EM field emitter is configured to generatethe magnetic field at a first frequency, and the EM sensor is configuredto: scan for unintentional radio frequency (RF) interference at thefirst frequency; and in response to a determination of the presence ofunintentional RF interference at the first frequency, switch to a secondfrequency that is different from the first frequency.

In a 58th aspect, the augmented reality display system of any one ofaspects 43 to 57, wherein the EM field emitter comprises an automaticgain control (AGC) circuit that is configured to: receive a voltagelevel for a coil in the EM sensor; and adjust a gain for anamplification stage of the EM field emitter based at least partly on thereceived voltage level.

In a 59th aspect, a method of operating an electromagnetic (EM) trackingsystem for an augmented reality (AR) display system, the AR displaysystem comprising a head-mounted AR display, an EM emitter, and aportable user-input device that comprises an EM sensor is provided. Themethod comprises emitting, by the EM emitter in the portable user-inputdevice, a time-varying magnetic field; detecting, by the EM sensor, thetime-varying magnetic field; determining, based at least in part on thedetected magnetic field, a pose of the EM sensor; determining, based atleast in part on the determined pose, virtual content to display to auser of the AR display system; and displaying, by the head-mounted ARdisplay, the virtual content. The head-mounted AR display may comprise alight field display.

In a 60th aspect, the method of aspect 59, further comprisingtime-synchronizing the EM emitter and the EM sensor.

In a 61st aspect, the method of aspect 59 or aspect 60, furthercomprising canceling magnetic interference from the detected magneticfield.

In a 62nd aspect, the method of any one of aspects 59 to 61, furthercomprising correlating real world coordinates associated with the poseof the EM sensor with virtual world coordinates associated with thevirtual content.

In a 63rd aspect, an AR display system operated according to any one ofthe methods of aspects 59 to 62. The AR display system may comprise alight field display.

Additional Considerations

Each of the processes, methods, and algorithms described herein and/ordepicted in the attached figures may be embodied in, and fully orpartially automated by, code modules executed by one or more physicalcomputing systems, hardware computer processors, application-specificcircuitry, and/or electronic hardware configured to execute specific andparticular computer instructions. For example, computing systems caninclude general purpose computers (e.g., servers) programmed withspecific computer instructions or special purpose computers, specialpurpose circuitry, and so forth. A code module may be compiled andlinked into an executable program, installed in a dynamic link library,or may be written in an interpreted programming language. In someimplementations, particular operations and methods may be performed bycircuitry that is specific to a given function.

Further, certain implementations of the functionality of the presentdisclosure are sufficiently mathematically, computationally, ortechnically complex that application-specific hardware or one or morephysical computing devices (utilizing appropriate specialized executableinstructions) may be necessary to perform the functionality, forexample, due to the volume or complexity of the calculations involved orto provide results substantially in real-time. For example, a video mayinclude many frames, with each frame having millions of pixels, andspecifically programmed computer hardware is necessary to process thevideo data to provide a desired image processing task or application ina commercially reasonable amount of time.

Code modules or any type of data may be stored on any type ofnon-transitory computer-readable medium, such as physical computerstorage including hard drives, solid state memory, random access memory(RAM), read only memory (ROM), optical disc, volatile or non-volatilestorage, combinations of the same and/or the like. The methods andmodules (or data) may also be transmitted as generated data signals(e.g., as part of a carrier wave or other analog or digital propagatedsignal) on a variety of computer-readable transmission mediums,including wireless-based and wired/cable-based mediums, and may take avariety of forms (e.g., as part of a single or multiplexed analogsignal, or as multiple discrete digital packets or frames). The resultsof the disclosed processes or process steps may be stored, persistentlyor otherwise, in any type of non-transitory, tangible computer storageor may be communicated via a computer-readable transmission medium.

Any processes, blocks, states, steps, or functionalities in flowdiagrams described herein and/or depicted in the attached figures shouldbe understood as potentially representing code modules, segments, orportions of code which include one or more executable instructions forimplementing specific functions (e.g., logical or arithmetical) or stepsin the process. The various processes, blocks, states, steps, orfunctionalities can be combined, rearranged, added to, deleted from,modified, or otherwise changed from the illustrative examples providedherein. In some embodiments, additional or different computing systemsor code modules may perform some or all of the functionalities describedherein. The methods and processes described herein are also not limitedto any particular sequence, and the blocks, steps, or states relatingthereto can be performed in other sequences that are appropriate, forexample, in serial, in parallel, or in some other manner. Tasks orevents may be added to or removed from the disclosed exampleembodiments. Moreover, the separation of various system components inthe implementations described herein is for illustrative purposes andshould not be understood as requiring such separation in allimplementations. It should be understood that the described programcomponents, methods, and systems can generally be integrated together ina single computer product or packaged into multiple computer products.Many implementation variations are possible.

The processes, methods, and systems may be implemented in a network (ordistributed) computing environment. Network environments includeenterprise-wide computer networks, intranets, local area networks (LAN),wide area networks (WAN), personal area networks (PAN), cloud computingnetworks, crowd-sourced computing networks, the Internet, and the WorldWide Web. The network may be a wired or a wireless network or any othertype of communication network.

The invention includes methods that may be performed using the subjectdevices. The methods may comprise the act of providing such a suitabledevice. Such provision may be performed by the end user. In other words,the “providing” act merely requires the end user obtain, access,approach, position, set-up, activate, power-up or otherwise act toprovide the requisite device in the subject method. Methods recitedherein may be carried out in any order of the recited events which islogically possible, as well as in the recited order of events.

The systems and methods of the disclosure each have several innovativeaspects, no single one of which is solely responsible or required forthe desirable attributes disclosed herein. The various features andprocesses described above may be used independently of one another, ormay be combined in various ways. All possible combinations andsubcombinations are intended to fall within the scope of thisdisclosure. Various modifications to the implementations described inthis disclosure may be readily apparent to those skilled in the art, andthe generic principles defined herein may be applied to otherimplementations without departing from the spirit or scope of thisdisclosure. Thus, the claims are not intended to be limited to theimplementations shown herein, but are to be accorded the widest scopeconsistent with this disclosure, the principles and the novel featuresdisclosed herein.

Certain features that are described in this specification in the contextof separate implementations also can be implemented in combination in asingle implementation. Conversely, various features that are describedin the context of a single implementation also can be implemented inmultiple implementations separately or in any suitable subcombination.Moreover, although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination. No single feature orgroup of features is necessary or indispensable to each and everyembodiment.

Conditional language used herein, such as, among others, “can,” “could,”“might,” “may,” “e.g.,” and the like, unless specifically statedotherwise, or otherwise understood within the context as used, isgenerally intended to convey that certain embodiments include, whileother embodiments do not include, certain features, elements and/orsteps. Thus, such conditional language is not generally intended toimply that features, elements and/or steps are in any way required forone or more embodiments or that one or more embodiments necessarilyinclude logic for deciding, with or without author input or prompting,whether these features, elements and/or steps are included or are to beperformed in any particular embodiment. The terms “comprising,”“including,” “having,” and the like are synonymous and are usedinclusively, in an open-ended fashion, and do not exclude additionalelements, features, acts, operations, and so forth. Also, the term “or”is used in its inclusive sense (and not in its exclusive sense) so thatwhen used, for example, to connect a list of elements, the term “or”means one, some, or all of the elements in the list. In addition, thearticles “a,” “an,” and “the” as used in this application and theappended claims are to be construed to mean “one or more” or “at leastone” unless specified otherwise. Except as specifically defined herein,all technical and scientific terms used herein are to be given as broada commonly understood meaning as possible while maintaining claimvalidity.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: A, B, or C” is intended to cover: A, B, C,A and B, A and C, B and C, and A, B, and C. Conjunctive language such asthe phrase “at least one of X, Y and Z,” unless specifically statedotherwise, is otherwise understood with the context as used in generalto convey that an item, term, etc. may be at least one of X, Y or Z.Thus, such conjunctive language is not generally intended to imply thatcertain embodiments require at least one of X, at least one of Y and atleast one of Z to each be present.

Similarly, while operations may be depicted in the drawings in aparticular order, it is to be recognized that such operations need notbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Further, the drawings may schematically depict one more exampleprocesses in the form of a flowchart. However, other operations that arenot depicted can be incorporated in the example methods and processesthat are schematically illustrated. For example, one or more additionaloperations can be performed before, after, simultaneously, or betweenany of the illustrated operations. Additionally, the operations may berearranged or reordered in other implementations. In certaincircumstances, multitasking and parallel processing may be advantageous.Moreover, the separation of various system components in theimplementations described above should not be understood as requiringsuch separation in all implementations, and it should be understood thatthe described program components and systems can generally be integratedtogether in a single software product or packaged into multiple softwareproducts. Additionally, other implementations are within the scope ofthe following claims. In some cases, the actions recited in the claimscan be performed in a different order and still achieve desirableresults.

What is claimed is:
 1. An augmented reality display system comprising: adisplay configured to project virtual images to eyes of a wearer; aframe configured to mount the display in front of the eyes of thewearer; an electromagnetic (EM) field emitter configured to generate amagnetic field; an EM sensor configured to sense the magnetic field,wherein one of the EM field emitter or the EM sensor is mechanicallycoupled to the frame and the other of the EM field emitter or the EMsensor is mechanically coupled to a component of the augmented realitydisplay system that is independently movable relative to the frame; anaudio speaker; a hardware processor programmed to: receive signals fromthe EM sensor indicative of a sensed magnetic field; and analyze thereceived signals to determine a position or an orientation of the EMsensor; and a noise canceling circuit configured to cancel magneticinterference in the sensed magnetic field generated by the audiospeaker.
 2. The augmented reality display system of claim 1, wherein thenoise canceling circuit is configured to: receive a first signal fromthe EM sensor; receive a second signal from the audio speaker; combinethe first signal and the second signal to provide a noise-canceledsignal.
 3. The augmented reality display system of claim 2, wherein tocombine the first signal and the second signal, the noise cancelingcircuit is configured to: (a) invert the second signal and add theinverted second signal to the first signal or (b) subtract the secondsignal from the first signal.
 4. The augmented reality display system ofclaim 2, wherein the audio speaker comprises a time-varying voltagesource and an amplifier, and the second signal is from the time-varyingvoltage source.
 5. The augmented reality display system of claim 2,wherein the received signals from the EM sensor comprise thenoise-canceled signal.
 6. The augmented reality display system of claim1, wherein the EM sensor comprises the noise canceling circuit.
 7. Theaugmented reality display system of claim 1, wherein the audio speakeris mechanically coupled to the frame.
 8. The augmented reality displaysystem of claim 1, wherein the display comprises a light field display.9. The augmented reality display system of claim 1, wherein: thecomponent comprises a user-input totem or a belt pack, the EM sensor ismechanically coupled to the frame, and the EM field emitter ismechanically coupled to the user-input totem or the belt pack.